I don't think I'd be all that excited to build a .300 Ham'r on a short action 700 or uni-sized T3 action. I'm not sure what the advantage would be going with an action that will easily accommodate a larger, more versatile cartridge like the .308 Win.
If I were building a bolt action .300 Ham'r, I'd want an action that's more svelt, like your CZ 527.
If being a lefty wasn't a requirement, I think a Howa Mini would do well.
