I would get a set of CAT main caps.
They probably are not as good as the milodon, but they are steel and that certainly is better than stock. Since you are going to have to line hone it any way, the CAT's probably will do fine and they are much, much cheaper.
I would just grab some stock caps for the front and rear. Since most people say a stock 351 block is good for around 600 hp, they should be enough for you. Also, if you think about it, the front and rear caps only have to be about 1/2 as strong compared to the center caps. The center caps have a crank throw on both sides, while the front and rear caps only have crank throws on one side.
I think a main girdle is serious overkill. Also, I believe they are designed to support the main webs, not the caps. Since you have a 351, it's main webs are already much stronger than a thin wall 5.0 block which is the one that has the main web failures.
Good luck.