Since we got a picture of the PTG reamer print I have modeled the cartridge in QuickDesign.
Guess what!
Easy to rechamber any 2.5" or shorter standard rim belted magnum or 308 based or shorter to 26 Nosler dimensions.
Looking very closely at the reamer print/QD model. It may have been something they set as a parameter for the design.
I made an entire series of calibers on the case dimensions. My goal was one head space gauge for all the calibers. It will work.
Then I spent hours of fun in QuickLoad and on JBM. The all calibers work from a ballistics standpoint.
How about a 458/26 Nosler gun)
All that is background to my recommendation:
Get any 264/6.2 barrel chambered or not that suits your desires/budget.
Get the reamer and HS gauges from PTG.
Take it and your action to your favorite GS and you should be good to go.
If I called ahead and dropped all that stuff off at my GS in the morning with a request for 'urgent', I'd have the barreled action chambered and head spaced back by the end of the day. Oh and he's good and cheap. I love the old curmudgeon.