yeah, I mentioned that in post 11. To the OP, if you have an issue with your engine or tune, do NOT try to compensate the problem by throwing gears, or anything else at it. IF you just want to move the car out of the hole, put a 8" 4800 converter in it. That should help it out under 3000 rpms.
Gotta wonder about the 904. Is it there because it was available, or is there because someone wanted a lighter transmission and did the work needed for it to survive racing and hard use?
Lots of good suggestions in this thread.
I'm with A-bodyJoe - install the diff already owned, and run it.
And with A/J et al to then adjust the timing and/or get better fuel.
Drive it and see how it is.
Honestly, if there was no time crunch, and there obviously isn't, I'd start with a simple compression check and then measure cam lift with a dial indicator and preferably a degree wheel.
