THouroughly inspect the heads before they are rebuilt. Worn valve stem seals and too much clearance on the valve guides can give you oiling issues that cause smoke on start up. As far as the block goes. You should have a number on top of the piston e.g. ,30 .40 etc this will tell you if the motor has been redone. Run your cylinders down to the bottom and check for a ring ridge at the top of the cylinder. If you can feel a ridge line you have wear. and should rebuild at some point. Check for carbon build up at the top of the cylinder where the piston ring stops. Carbon here can indicate oil ring failure. run your piston down half way and wiggle the piston. If you have slop you have worn rings. You should not be able to move your piston more than .003 - .005 thousands. If you can do more rebuild. You certainly have nothing to lose other than a little time and a set of gaskets to rebuild your heads and reinstall to see if your oiling smoke problem exists. P.S. Black smoke is too much fuel and white smoke is oil. Make sure that you had white smoke before proceeding. If it was black it is carburation. Cheers,

if top of cilinder has a ridge that stops at top of ring travel. there is wear .(oversize) run piston to bottom of cylinder and use an inside mike to see if hole is round as far down as posible .not a true test but will let you decide how far you want to go.look for scratches in cyl for sign of broken rings.