smokes when starting

Just finished rebuilding the engine on my '91 5.0.No machine work,just re-ringed the pistons,honed the cylinders,new rod & main bearings.The lower end is bone stock with stock cam.I added a set of Edelbrock performer heads(used),performer intake,65mm throttle body,73mm C&L mass,24# injectors,FRPP roller rockers,and 1 5/8" headers.The car runs great,but when started has a puff of smoke.After that no smoke and runs great.I suspect valve seals because I bought the heads used and like an idiot installed them without taking them apart and checking them.I pulled the plugs and found that #4 & #8 plugs had signs of oil on them.My question is before I spend an afternoon replacing valve seals,is there anything that would cause the rear plug on each side to get oil fouled or is this just a coincidence?

found the problem

I decided to replace the valve stem seals.First step was to pull off the upper intake.Guess what I found?The intake was full of oil!!Come to find out ,the lower intake (where the pcv plugs in)has a metal plate(oil baffle) rivetted underneath.I bought the intake(edelbrock performer)used and it was never installed.Oil was being sucked through the pcv into the intake.Iremoved the intake and installed the baffle from the stock intake.Problem solved.