Help with smoke from a 400
 

Have a 74 400 that smokes intermitently out of both tailpipes. Seems to get worse as it warms up. The smoke is a grey. Doesn't burn your eyes so i'm thinking it's not fuel.
Background: Motor rebuilt by previous owner(Don't know much about inside. Very clean under valve covers)
Any ideas on where to start? I don't know alot about Pontiac Motors to know if there are common areas to check.
THANKS for any help

blue/gray smoke is burning oil

possibilities

oil leaks on motor dripping on exhaust pipes, usually from valve covers, engine or transmission oil pans. Smoke from oil on hot pipes can appear to be coming from tailpipes while going down the road.

problem with PCV

piston rings worn out or if new not sealed at breakin

worn valve guides or damaged/improperly installed valve oil seals

bad vacuum modulator on auto trans

and possibly one or two other suspect areas Im not thinking of right now.

Thanks for the info.
Anothere thing to add. All the plugs show the same Black color, not wet. No one cylider is any worse or better than the other.
Did a complession test(while warm) and all cylinders range from 145-155 PSI.

A motor that runs way too rich can cause oil burning b/c it washes the oil film off the cylinder walls. Can damage pistons and rings from lack of lube.

Could be that the oil rings were installed wrong, so thats why it's pumping oil but has good compression. Could also be overfilled with oil, too thin a weight, etc. Valve guides/seals a strong possibility. Puffs on startup, idle and deceleration are common with worn guides/seals. It's worth making sure the top end oil control is right. It's common to rebuild a motor and totally overlook oil control in the heads due to work guides, valve stems or incorrect seals. The result is a strong running smoker.

The first thing to check is what kind of oil control are being used on the heads. Come to think of it, the stock O-ring and deflector system sucks. A set of the blue vitons would be much better, if they'd fit the guides.