Only dealt with 4 bolt mains but I have a 2 bolt main 350 and wanted to know if there is any way to reinforce it to handle higher horsepower 450 to 500. I have been told there are girdles out there to strenghten it. Just looking for some other opinions.  

you can have splayed main caps installed.  that will make it a 4 bolt, and from what I understand it will be stronger than a factory 4 bolt main block.

The least expensive and quite effective method is to use studs and a girdle. This will require machining the main caps flat across the top, but you'll probably not need to align bore unless required to correct block warpage. This goes a long way toward keeping the caps from shifting sideways as well as fore and aft. They don't add much to block stiffness and don't transfer tensile loads from one cap to any other.

4 bolt conversion caps help add tensile load capability to the center main caps but don't do anything for 1 or 5. They don't stiffen the block and they don't do much to improve side to side or fore and aft shifting. They always require align boreing.

The best is to use both, if this engine is expected to deliver 500 horsepower continously in a competition setting, a girdle and 4 bolt caps go a long way toward insureing the bottom end doesn't come out. For the occasional excersion to 500 hp either one will work.

Bogie