Cz 550 .375 bolt face caliber options

[k128]

I just won an auction for a cz550 safari classics complete magnum receiver with a 375 h&h bolt face. I've never had a rifle built before, but I know the easiest (read cheapest) thing to do is a bell and carlson, and have the action fitted with a caliber thats h&h based. I've already got a 375 h&h and a 416 rigby. I want to go as large as possible and i think the 458 lott is essentially the largest for the bolt face if I'm not mistaken? I'd love to go .500j or 505 gibbs, but does the bolt face/extractor have enough meat to machine to the case head specs?