If you are wanting a crate type of performance engine that Reher Morrison 622 is hard to do better.
Reher Morrison will not build anything above a 622 cu in engine with a cast iron block in their Super Engine Series. Years ago Reher Morrison did offer a 632 cu in engine just like everyone else did. By decreasing the stroke some and increasing the bore some thay came up with their 622 which blew away their 632. That is why they will no longer sell them. As many 632's as there is and as I have built, I am convinced the 622 is far better. Check the performance on the Reher 622 before you close the door on it. REher will build up to a 880 cu in if you have deep pockets.
There are several good engine builders in Louisianna and a whole ton of good Custom Engine Builders in Texas of which I try to be one of. There are also other crate builders other than Reher Morrison. Sunset Racing Engines is another one.
It all depends on your budget, time limits, and what you want.
Ed