I've been using flat tappets with success but 2 things I do.
I have been nitriding the camshafts, and I run lifters with direct face pressurized oiling. Meaning the face of the lifters are drilled and squirt oil directly on the cam lobes.
This does add to the cost, lifters are usually around $300 and an additional $150 on top of the cam price to have it nitrided.
Still cheaper than a retro roller upgrade if you really don't want that. Nothing against rollers here though as I use them in a couple other engines.
On our 69Z I had a custom solid flat tappet grind done to mimic the original cam with a couple minor changes in lobe design, nitrided it, and run Comp EDM solid flat tappet lifters to oil the lobes. So far we've logged over 50k miles on that engine, I check the lash at oil changes, and after over 5 years the lash hasn't budged. Very happy with it.
When it comes to hydraulic flat tappet lifters, I like to use either Rhoads with their pressure lube option, or the Crower with the pressure lube option. Those have treated me well.
As far as cam grinders, or more specifically a smart guy that knows his cam lobes, I prefer to use Paul at Koerner Racing Engines in Tucson. Paul and Jeff were close friends to Harold Brookshire and they have access to many of his lobe designs that were given to them when he passed. He generally uses Lunati to grind them, which is owned by Comp. They have had some success at the EMC competition and build most of the Nascar SW tour engines out here. Consequently I use them for my machine work as well.
Bullet is another great place to go and has a lot of Harolds older designs from his Ultradyne days.
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