So you are certain the rotor/distributor is turning? That would rule out timing chain.
Perhaps the module you put on is defective. To get volts to the distr w/ key on and not get spark at the plugs means it is something in that distributor that is malfunctions, but, they are quite simple devices.
I've mentioned this many times, but, you can go to a salvage yard and get an entire distributor, module, coil, rotor, cap, p/u coil---the whole nine yards for about $20 probably. I keep an extra HEI in my garage at all times. No spark? take 15 mins and switch distributors. All sbc HEI's are interchangeable; 305, 350, 400.