Economical replacement rocker arm set?

Yes, you will be able to see the cam to some degree from underneath; you may need a mirror to see all the lobes, and the crank will have to be rotated a couple of times to see all the lobes.

So if you used Mobil 1 synthetic, then it does not have the ZDDP levels usually required. (Check out the chart linked...)

I can't find the exact ZDDP levels of the AMSOil Zrod 10-30, but all their literature indicates that it has adequate ZDDP lifters for flat tappet cams.

BTW, just for edification..... Mobil 1 IS petroleum oil. It is very highly refined petroleum oil; IIRC, it is refined to get highly consistent molecule sizes. That gives it its particular properties. So changing from Mobil 1 to a 'typical' dino oil is not changing TO a petroleum oil; you already have it.