Hi CSL DART,
Looks like you got a good foundation to start with. 400hp out of a 360 is easily doable and if you go that route, i would recomend going internally balanced on the engine. It opens up a world of different torque converters and harmonic balancers you can use over stock externally balanced, however you might also concider making an internally balanced 408-410 stroker out of that 360. I am going that route with my 67 notchback cuda. Reason being is you can run a little less aggressive cam, and compression with the stroker than the 360 and still achieve your 400hp goal. This will give the engine a bit more "manners" and act a little more civilized. I would recommend staying away from the big block only because its going to add weight unless you put it on a severe aluminum diet, plus making it fit. Its a fairly tight fit for a small block.
As far as the suspension goes, most guys when the rebuild their stock front ends looking for a better setup typically add tubular upper arms, box in the lower arms, add polyurethane suspension bushings, and a bigger front swaybar than stock, as well as upgrade the shocks. Steering if your running a saginaw power steering pump you can get more road feel by dialing down the pump pressure. There is a thread on here called pump it down easy . It details how to lower the pump pressure to eliminate that overassisted disconnected feel leaving enough assist for parking or low speed turning.
Your brakes in the front have been converted to BBP disc already as evident by the cop wheels. However if you want bigger discs on the cheap, look no further than 78/79 disco era B body cordobas. Their rotors are almost 12" diameter. These are a bolt on to your dart disc brake spindle. You will also need to source the cordoba caliper brackets and longer caliper bracket bolts to do the swap. Your pads and calipers will fit right back on. Additionally the cordoba calipers use a larger 2.75" dia. piston VS the dart 2.60" dia. one. If you cant find cordoba calipers M body dodge diplomat fury fifth ave from 84-89 also used a 2.75" caliper and its a bolt on as well.
On the rear, and i have been through this. A dana is a good choice but if your thinking Dana 60 its heavy and costly. More better suited to drag racing. An 8&3/4 is also costly. I had to piece mine together and have about $1300 in it including all the swap n trade BS i went thru to build it. My sons 69 we are putting in a ford exploder 8.8 this by far is the cheapest way to go for a good strong rear. The sport trak ones being the ones most guys doing this swap look for. It has the same wheel pattern as mopar BBP big bolt pattern , comes with a locking differential, 3.73 gears standard, and rear disc brakes. The mustang guys use em and theres lots of gear ratios available, C clip eliminators, rebuild kits for the lockers are about $60 with a new cross pin bolt and friction modifier.
There is a thread in here about installing the 8.8 and hooking up the parking brake, how to cut it down to fit, which U joint to use to mate it to the mopar driveshaft, master cylinder to use etc. Some come with an open diff, so look for the L on the diff ID tag. It will give you the gear ratio as well. Example 3L73 is a locker with 3.73 gears. I payed $300 for one complete end to end off a FB trader page needing brake work, though some guys have gotten em for $150 with a.complete brake job already done. Rotors are dirt cheap for $15 each new at rock auto and not worth turning if warped.
On the trans i would recomnend a 46RH from a dodge pickup over a 727. A 46RH is a 727 variant with an overdrive. This allows you to run a set of 3.55s, or 3.73s and hit the O/D button or switch when you get it on the freeway. So around town you can have fun, then cruise on the freeway. 46RE is electronically controlled so dont get one of those it needs a computer. An alternate is the A518 which is an A904 with a full lockup converter. Both of these transmissions will require modification of the car for the rear mount.
I hope this gives you more options in the direction of your build.
Matt
