IMHO, a roller would be the best way to go since flat tappets are prone to lobe failure unless you're very cautious about the break in procedure and then it's still a crap shoot. If you're going to run a flat tappet use worn out valve springs for break in and a good oil additive with zinc and don't tighten the rockers too tight on start up.
I don't think that the quality of steel is what it in the 50's and 60's and that along with the lack of zinc in today's oil is a death sentence for flat tappet cams. If I was going to go that route I would be looking at Isky, Howards, or someone like those two who have been grinding cams since Christ was a corporal.
I have an Isky 30-30 ground in 64 that has been in a couple of engines that I wouldn't be afraid to use again and probably will.