Sorry I missed this one to this point, I'll see what I can add.
First, avoid drop spindles like the plague. They are totally useless on a car running larger torsion bars, and they add bump steer. If you have large diameter torsion bars (and it sounds like you will), then you can lower the car with the torsion bar adjusters. Yes, that changes your suspension travel which is why you should also replace both the upper and lower bump stops. The upper bump stops need to be taller, the lower bump stops (on the LCA) need to be shorter. Do that and you will have recentered the suspension travel around your new ride height. The ideal ride height for best suspension geometry is when the upper control arms are roughly parallel to the ground. That represents a good 1.5" to 2" drop compared to stock, which is fine with 1.12" torsion bars. The Firm Feel 1.12" torsion bars have a 300 lb/in rate, which means they're almost 3x stiffer than stock. Which also means they need a lot less available travel. On my car, with my shortened lower bump stop, the suspension at full compression puts the spindle 13" away from the inner fender. Which means even with standard spindles and a 26" tire you will run out of suspension travel at the same time the wheel hits the inner fender. Or in other words, you can't add more travel with a 2" drop spindle.
Based on what you've done to the rear end, I would say you should skip the QA1 and Hotchkis UCA's. The QA1's are not adjustable other than the eccentrics, although they do have more caster built in. Which is fine for most street builds but it seems like you're going for more of a track/autoX set up. I would recommend a set of SPC UCA's from BergmanAutoCraft
BAC SPC Upper Control Arms - Bergman Auto Craft
The SPC arms are double adjustable, meaning they can be adjusted on the car without removing anything (unlike hotchkis). The BAC version also has delrin bushings, which are far better for a car that will also see street time than heims. On my Challenger I run Hotchkis UCA's, the first set of heims only lasted 7k miles. The second set might make it to 10k, but with 7k on them too they're making noise. Heims at the UCA are no good on the street. Strangely enough they seem bulletproof at the strut rod, the QA1 style adjustable strut rods on my Challenger have 70k+ miles on them and the heims are fine.
On that note, you want adjustable strut rods. The QA1's are aluminum and very nice, and they last a long time (70k and counting). Adjustable strut rods are necessary in my opinion whenever you use poly or Delrin LCA bushings, and on any serious corner carver. They let you tune the length of the strut rod so there is no binding in the movement of the LCA. On my cars after I set up the new bump stops I leave the shocks off and the torsion bar adjusters out so I can raise and lower the suspension through the entire range of travel when I set the strut rod length so there's no binding at all at the LCA.
I would use Delrin LCA bushings at the level of build you're doing. BergmanAutocraft has them, I installed the ones on my Duster with Firm Feel's greaseable LCA pivot pins. The Delrin is supposed to be self lubricating, but the fit from the pin to the bushing is very important because there's very little give in the bushing. My FFI greasable pins were by the far the best fit, compared to both stock and other aftermarket pivot pins.
Sway bars- at your level of build, I would honestly sell your '67-72 sway bar tabbed LCA's and either buy a plain set or a set of QA1 tubular LCA's. Reason being is that the 67-72 sway bar tab location and the sway bars that go with them limit tire width. If you get a Hotchkiss front sway bar they use a custom location for the tabs, which is basically a 73-76 sway bar tab location. Same for the Hellwig "pro touring" front sway bar for the 67-72 cars. Your tabbed LCA's will bring a good amount of money, so buying a plain set would actually put you money ahead. Or you can get the QA1 LCA's. Their tubular design has a lower height profile, which basically adds about 1" of travel back into the suspension. Their new design has bump stops integrated into the LCA that remove that advantage, but they appear to be easily removed.
I run the Hotchkis Fox shocks on my Duster with the 1.12" torsion bars. They work great. Mine are even the non-adjustable version. I have also run Bilstein RCD's on my Duster previously. They worked well, but the Hotchkis Fox's are better tuned to the 1.12" bars than the Bilsteins were. I have a feeling the Bilsteins are set up more for a 1.03" to 1.06" bar. Totally still better than a lot of other options, but the Fox's are better for the 1.12's.
On the front you can get up to a 275/35/18 for a tire, the most hassle free rims would probably be 18x9 or 18x9.5". 18x10" has been done, but clearance to the UCA starts to be more of an issue. I run DoctorDiff's 13" cobra style disks on my Duster, with those on the FMJ spindles I have I run an 18x9 with a +35mm offset. The 13" cobra style brakes work very well, I previously ran 11.75" mopar disks on the car and they were an improvement for sure. Lighter too with their aluminum hubs.
The only thing I really see you kicking yourself over is the transmission. 3.55's will be fine for autoX, but on a long track even with 26" tall rear tires you'll have to be turning at least 7k to hit 150, and that's ignoring drivetrain loss and aerodynamics. I run a T56 with 4.30's. But with a .63 6th the gearing would be good for 170 @6k, although the aerodynamics would likely limit it before that. My 340 isn't really built to turn more than that though. To be honest, I think it might be cheaper to build a more standard stroker and pair it with an overdrive transmission. Building a 340 that will live happily on the street and turn 7,500 rpm is gonna be pricey, and the driveability around town will suffer.
Also, a lot of the installs on the parts I talk about are documented in my build thread, which has a link in my signature.
. But that depends a lot on use too, if it were just a fun "weekend car" I could run 3.73s or 3.91's and not worry about the freeway cruise as much. And I wouldn't be stuck in traffic as much either. But as my daily that issue was definitely more noticeable.
