I performed a piston to valve clearance on my 383 today. I don't think I need to go through the steps, but one thing I did I'm not sure of if it was right or not.....did I need to pump the lifters up before doing this check? I ask because I didn't pump them up, just put some assembly lube on them and performed the check as normal. Not sure if with the lifters pumped up how much it would affect my calculations.

Pistons are 2315's @ 0.005" in the bore, XE268 cam, I calculated .1755" of clearance NOT using a head gasket, just snugged the head down to hold it in place.

Anybody think I messed up by not pumping up the lifters beforehand?

did you use checking (lightweight) springs?
if not, you probably needed to use a solid lifter. if the plunger in the hydraulic lifter compressed you will not have an accurate P/V clearance.

Yes need to use light checking springs and I'd suggest a pair of old hyd lifters w the cup epoxied to the top of it's travel. Solids have a deeper "cup" but to measure V/P clearance due to the "lift", measuring it w the diff cup depth may actually b OK & the same in effect as measuring it w a diff length pushrod but the diff "cup" depth MAY or may not affect the wipe pattern (I'm not sure) if you checked that also so short version I'd use an epoxied hyd & then you'd b good on everything unless someone chimes in that the diff cup depth does not affect your outcome.

silicone sealer works good in a hydraulic too

Thanks for the info. I epoxied a few lifters so we'll see what the difference is tommorrow after I get home from work.