I have a ZKK602 in 375H&H that has been used many years. It finally split at the recoil lug. Glassbedded it and it's still performing well. I have a new 550 in 416 Rigby and it has one crossbolt a better barrel recoil lug and grooving on bottom of action to better grip the wood and
better recoil lug bedding. I don't really see how you could greatly improve on it. Only thing I might do is glass it.