Tim,
Thanks for that info! I thought I had read that hydraulic lifters did not appear until the '53 Powerglide 235 with the full-pressure oiling; after checking the link you shared (and confirming with the 1950 car shop manual supplement), I stand corrected.
Strange, though: the valve train on this engine is noisy as hell, though (I just got it running about a week ago and haven't adjusted the tappets yet), so that also fed into my assumption that they were mechanical. Perhaps I have a collapsed hydraulic lifter or two in there?
At any rate, I've got to patch up or replace that oil pan before I get back to tune-up work!
