Pinion Angle/Tailshaft Bushing

Yeah that is what I kindof suspected.
I once put a 340 cam and Xheads into/onto an otherwise stock 73 teener. Yeah with 2.76s that was a bit of a disaster. It had great passing power on the hiway, but out of the gate,To say it had"slightly less low end torque" would be too kind. It flat out sucked. The addition of a 2800TC improved things a bit. But when the 4.10s went in well, that was the magic. I won't ever do that again.
When that Dart died, I pulled the powertrain and junked the rusted hulk, which today would still fetch good coin. But in the late 80s who could have known.....
So fast forward 20 years or so, and in 2000 I un-mothballed that same engine.I yanked the 340 stuff in favor of the teener equivalents. I freshened up the rings etc. and plopped it into my FormulaS clone as a winter engine.( I used to pull the 367 every September and go thru it in the snowy season). Some years it had an auto, and some it had a stick. Sometimes a 3.66 low and sometimes a 3.09od and sometimes a 3.09od and a GVOD for a double od. One year it had that 2800TC and 3.55s . Of course it had the TTIs on it and a small-port intake with a TQ on it. It was still the 8point something factory compression.And I put some 360valve springs in it, (or 340, not sure), with the 273 rocker gear. I still have this engine.
Well I'll tell you, that lil teener surprised the dickens outta me.Best lil teener I ever had. It was so sweet, I just hadda mess with it. Every May I pulled it out and stuck the freshened 367 back in. So then,I would contemplate the next winters combo. One winter,I put an A999 in it with the wide ratios and a semi-auto shift kit in it, that allows both auto mode and full manual. And then, Then, I put 2.76s in it.
Now if you have never heard a mellow 4 barrel teener running WOT, in high gear, from 20mph to 65 mph, screaming obscenities at me through full-length dual 3 incher exhaust and Dynomaxers, Man; I can't tell you how sweet that sounds. That is just one long pull at one rpm!
I used to nail it from a stop, get her into 3rd by 20 or earlier, and then, let that TQ moan, for what seemed like forever.65mph was still near 2800.Hyup, that brings me a huge smile just remembering it. The starter gear with the A999 was 7.56, and with a 2800TC, and with the teener top-end back on, she had plenty enough giddy-up for a winter motor.That combo pulled about 75/80 mph still at 2800ish.
I mean imagine the dyno-operator pulling the stick, and keeping the Rs at 2800 for about 14 seconds,lol. That poor teener! I used to torture it so bad.
One winter I had the od/GVOD combo in it with 4.30s I think. That teener pulled the od ratios all by themselves, but I had set the GVOD up as a splitter. The starter gear was 13.29, and double OD was 2.45. Well with that starter gear, the teener hits shift-rpm real quick. I used to shift it at 5000; sometimes 5500, just because.
First topped out at about 30mph,and 1st-over at 39. Second was 56, and 2nd-od was 72. Third was 94, and 3rd-od was 120. But I rarely went past 72@5500; That was 4 ratios........ 65mph was a tic under 2000,lol.
I gotta tell you, a teener with 4.30s, and split-shifting, is pretty neat.
Those winter combos were not fast. Nor quick. But it/they were hands down,the funnest I ever had. They were not about being fast or quick. They were just about being mellow.
I stopped doing that after the 5th winter or so. The 367 was no longer having issues, that I was catching in the nick of time. And she was in her final iteration. I was no longer broke; the kids were on their own, and doing well. I bought a second car, and no longer needed the S for winter. Hallelujah, no more swapping powertrains.
I still miss that teener now and then.............
But 93 in the 1/8 is funner,lol

That all sounds like good fun to me. I've had some good street fun with nice mild 318s. Mines a little rough revving as mentioned, but I think a lot of that is just poor quality replacement motor mounts.

Drove it out to Van Nuys Blvd cruise night tonight and still out right now. Came to conclusion with my phone speedo that 70 mph is 2500 rpm. And actually, the vibes seem to smooth out at that speed and rpm. 2200 is more like 62 mph where it's still a bit rougher on the occelation/resonating vibe.