So what? They need guides and a valve job? I have yet to see a set of heads Id let out the door with the valve job it came within. Not one.
So there is nothing wrong with the castings, they just need to be rebuilt.
Why new valves? Are yours junk? Or do you not want 3/8 stems? Not sure why you think you need aftermarket retainers. A set of springs for what you sound like you are doing is pretty cheap.
Im just trying to get my head around what you are doing.
I suppose given what you've posted, I’d pick the SM heads, but they would get a valve job. And probably a surface. Most of all new heads don’t have that flat of a surface.
