A few weeks ago I installed a 200R4 in my 69 Skylark. Everything went well, took some drive until I got the TV cable correct. When completed it was shifting great; earlier today I went for a ride and couldn't tell if it was shifting or not however, when I slowed down and stopped I could feel the transmission down shifting. On the way back home it started shifting where I could feel each gear. Was the trans shifting and I just couldn't tell before?
Do you have a lock-up torque converter? If it was a high stall lock-up it's sometimes hard to tell when it's shifting. Put the converter in forced lock-up and you should be able to hear and feel it.
Depends on how you use the car. Some that race a lot go with non-lock-up converters as they don't break as often under stress of racing. But, there are lock-up converters built for racing; very expensive. For street use even with high horsepower, I would recommend a lock-up converter. They run cooler and give better fuel mileage.
Pretty much have a stock 300-4 with headers and a isky 262 cam, 3:23 posi rear end. So more cruising than racing for this car.
What transmission do you have in the car now? If you have the original ST300 auto, there is not a lock-up converter available for this tranny. If you have or go to the 2004R overdrive tranny, there are lock-up converters available for them. But, your 3.23 rear ratio may be a bit too low (numerically) to use the overdrive feature. The RPM in overdrive might be too low and the car may lug in 4th gear. The effective ratio in overdrive would be 2.23. You would probably want to go with at least a 3.73 or even a 4.10 rear with the overdrive tranny.
Just a little bit of info here. I had a 200-4R behind my 300 (Ported, Cammed Etc.) in my '65 Skylark. I had a 3:55 rear gear and I was cranking 2 Grand at 70 mph in OD/Lock-up. Jim (Ponch)