First I would do the rear end. And 8 3/4's are getting expensive and overrated in my opinion. For the same price you could do a Dana 60 and have more than your car will ever give it.. (3.55 gears)
Working my way forward the transmission. The 904 is plenty strong for 10 second cars so just rebuilding it maybe with some heavy duty Parts would be more than adequate and lighter and less paretic drag as well...
And for the engine if you want to keep numbers matching and have lots of streetable power I would just do a stroker kit and have a 390 Stroker. It would just have gobs of off the pedal torque and you could even put a relatively mild cam in it and have everything you want...
My-2..
