Will the 700r4 from my 90 T/A bolt up to a gen 1 383 ? I read somewhere that the crank flange lenght is different and you need some sort of adapter. Thanks for any help...

Your 90 is a Gen I
All SBC ( inc Gen II LTX ) engines have have the same bellhousing pattern

1 pce seal engines > '87 ( like your 90 ) have a different bolt pattern on the crank flange to the earlier 2 pce seal engines.
All you need is flexplate that matches your new engine

Thanks for the info..

How do you plan on using the torque converter lock up feature?

If you use the stock induction/control system, the TCC lock-up won't be a problem.

I plan on retaining the lock up converter. The main reason for my question was that I read somewhere that the crankshaft flange lenght is different on the older chevy small blocks to the point where i might need a thin spacer mounted between the block and the trans to keep clearance between the converter and the trans.. IDK ? Thanks, Patrick.