Dear Dennis;
Flat tappet lifters/cams wear faster that 'stock' because of the higher spring pressures and the way they (high lift) are ground. This is why the 'roller lifter/cam' was developed for racing.
The "flat tappet" lifter is actualy convex (new) flat (worn) and concave (junk). A 'junk' one will "eat" that cam lobe.
Dello oil is mostly run in (big rigs) with diesel engines, under extream conditions and just slightly more $ than 'consumer oils'.
Another thing is to; check the lifters regulary with a straight edge, which is how it was done in the 50s, long before government intervention.
Good luck.
