I have rebuilt my 67 mustangs 289 v8 engine because of lack of power and trouble running. I did some basic upgrades(rocker arms, electric fan, electric fuel pump) but nothing huge. I replaced all the gaskets and almost every part or the engine. I started it and drove it a small distance after a long warm up but there was still a large amount of white smoke from the tail pipes. ecxept for piston rings and valve seals can you think of anyother reason for this? Thanks