I think this is all about 5 year old news. Had FE hydraulic rollers around for years now and the
oil deal has been a problem for at least that long. Use the correct break in
oil and procedure with the flat tappet and then the correct
oil after you install in the car and you will be fine. Like Barry says done right the flat tappet will be fine.
There have been several companies making hydraulic roller lifters for FE s now for several years. We have seen a few problems with al of them but we handle a lot of parts. We use the Morel lifters mostly now. Had used the Cranes till they went under and now they are back up running. It seems that with this engine stuff you can get a bad part at any time and that is what gives us the most problems, a bad part.
Like Brent says you can get about any kind of hydraulic roller lobe you want but you better know what you plan on doing with the engine, the weight of the valve train, spring used, rpms desired and so on or you can get yourself in troubler.
Good luck, Keith Craft