I put a new flat tappet cam in my Monte Carlo in 2010. I bought the cam and lifters in the mid 1990s. I used full synthetic oil to hopefully minimize wear. I have had no issues. I used a proper break-in oil and procedure.
I agree, there is a lot of discussion, and the common theme includes use of a new cam and lifters. Some claim the lifters are remanufactured or that the taper on the bottom of the lifter is wrong, and others blame the lack of zinc additive. In the early 1980s, GM had a problem with bad cams losing a lobe due to improper hardness.
A retrofit roller cam and lifters are pricey, and you also need to have a cam button since your block is pre-1987.
I don't recall you changing your cam. Since your cam is already broken in, I feel if you use full synthetic oil and you will be fine.