The LBZ rotating parts will all interchange with LB7 rotating parts. The issue runs into balancing. Keep the balancer and flywheel matched to the crank. LBZ crank, use LBZ balancer and flywheel.
Rods and pistons wont matter each way
Are you sure? I thought the LBZ/LMM has a longer piston skirt.
From what I understood, LBZ/LMM crank+any year pistons/rods = OK
-but-
LB7/LLY crank = LB7/LLY pistons only. LBZ/LMM pistons will hit the counterbalancer on the crank. Rods are all the same as far as dimensions go.
I might be wrong on this but I remember we had piston issues with Simon's truck that resulted in some fancy machine work to make everything fit.