stock camaro mm will mount the motor real low in the engine bay
i'd install the cab to locate the motor near the stock location
this location may be high enough to center the motor in your clip
imo... a level carb is good, up or down a few degrees is ok too. don't focus on a level carb, focus on what looks/fits good
how many stock vehicles have been raised a few inches in the back to accommodate big wheels. they run fine
without the cab on the frame i'm not sure how anyone could finalize the motor/trans location
i left my cab on until the suspension, motor mounts and ifs was complete