You do not want solid lifters. They require periodic valve adjustment. Solid roller lifters have a short life and a very short life if the valves are not adjusted properly.
FE rocker arms require better than OEM, when heavy valve springs and high lift cams are used. Not all high performance rocker arms are a good setup. You want a good builder who know what works and specializes in FE engines.
The factory blocks have a poor
oil design. A good builder, who specializes in FE engines, knows what modifications to make.
The factory blocks were designed for a rope seal on the rear main seal, so cutting the groove did not require a perfect circle on the same center as the crank. Modern seals do require a near perfect circle on the same center as the crank. A rope seal is designed to slow a leak, but cannot stop it from leaking. If you pack a rope seal too tight Friction will heat the crank until it turns blue. There are several other places FE engines are prone to leak from. Very few FE engines are leak free and most of those will leak sooner or later. It is just a matter of how bad will the leak be.
If I wanted an FE I would not go to a mass produced engine shop. I would look at a smaller, detail oriented shop, that specializes in FE engines. Blykins who just replied above, is such a shop. The link to his website is in the footer of is reply.
Honestly from some of what you said, I am not certain a FE is what you want. All engines have some issues, but the FE was designed in the 1950's. To say it is not in the same ball park as a modern engine is an understatement. It's more like a baseball park compared to a tennis court.