pros and cons of a flat tappet cam

I have heard the "8% mileage improvement" claim for roller cams, which is probably true, but I doubt the reason is due to reduced friction alone. I suspect the improvement is mostly because with a roller cam one can have a more optimal profile.

After-market link-bar roller lifters are very expensive. I wonder if one could use standard Magnum engine lifters with the spring-plate lifter retainer by tapping mounting holes in the block (during a total rebuild). Seems I heard this, but have never seen photos or "I did this" posts.

Failures with flat-tappet cams are probable due to a combination of factors. Many people run much higher than factory spring loads. Metal treatment of lifters and cam might be suspect, especially with so many parts made outside the U.S. today. Less additives in oil today. If the latter, I wonder why many other current engines don't have failures today. I have 80's and 90's cars (OHV cams) that have similar sliding surfaces. Indeed OHV cams fail much quicker from oiling problems, but it doesn't seem to be endemic today.