Fishhawk

I would suggest the R block over the Mexican block. There really isn't a HO version of the Mex. block. It was orignally built for taxis and some trucks. Definitely stronger with larger webbing, etc. However it is not a roller block and will be harder to find. I'm not sure but I don't think the Mex block is a 4 bolt main block. The R block is.
Why not the 331? Should last longer which also means it should take more of a pounding.
PS .... the girdle is a waste of money. All it might do is keep a few of your parts together after you crack the block.