A year ago I bought an used T56 trans complete with belhousing, flywheel clutch etc.
I'm now going to install it in on the back of a initially auto trans equipped '92 mod 5,7L motor.

In the Camaro and Corvette tech book it says that prior to disassembly there must be put marks on the bellousing, pressure plate and flywheel in order to put this back together again the same way it was.

There is a yellow mark on the pressure plate but I can't find any mark on the flywheel. And obviously I will not be able to put the flywheel on the crank according to marks on the bellhousing.

What do I do now?

 

Don't worry about it. Just put it together.

Each of the pieces is supposed to be correctly balanced. If they are, then it makes no difference what goes where. The flywheel will only go on the crank one way, so it takes care of itself; and the clutch is supposed to be neutral balance.

The mark on the BH is supposed to be for reference, so you put the flywheel back on the crank in the same orientation. Which might matter on a 2-piece RMS motor, but not a 1-piece. Sounds like that instruction is an "appendix" left over from an earlier edition; had meaning at one time, but now is useless and doesn't apply.