Just bought a 1970 Mach with 351 Cleveland.70k Original - never been touched. Smokes at start up and when runing assuming it is valve steam seals - how difficult are they to replace, I heard there are way to replace w/o removing heads.

 

pull off a valve cover & see if they are all broke up, not that hard to replace, get a haynes manual, you can do it without pulling heads, you will need to keep valves from dropping into cylinder either with compressed air through spark pulg hole or my favorite trick a few feet of string fed into the cylinder then turn motor by hand til piston with string on top hits valves & keeps them in place.