Hi Bob,
I had a Win classic 300 RUM model 70 built. My smith had to open the bolt face a tad but other than that it was a rebarrel.
If you have a good smith to work with a pre-64 would make a nice rifle.
I think I messaged you a picture of my 404. The 300 RUM makes a nice conversion.
I already had a 375 H&H so I wanted something a little bigger.
Go for it.
Roger
My M70 404 Jeffery