I would find the correct ball bearing and put back in there. It may or may not be your issue, but you need to cover all ground to eliminate all possible problems. The too tight valves may cause a pop like that. I use the 1/3 turn after the rocker is quiet method, but 1/2 should be fine. I have even lashed hydraulic cam,s at 1/4 turn with good results on a smaller cam. 20* initial is good, but I like to see about 35* total all in by 2500-3000 with vac advance hose unhooked and plugged. 50* is fine cruising, but you might want to try driving with it unhooked just to see if it has too much timing cruising, that can cause over heating. I did that once on a 69 roadrunner with a original 383 4 speed. Too much timing over heating it and I couldn't figure out why, but was told too much timing could cause over heating. Motor blew a piston before I found that out. Sure did run good thought. I was 18 then and didn't know any better.