What are the specs on your new build. what caliber is the original rifle?
Change from 308 to 25-06.
Watch feeding. The rails are part of the receiver in the pre 64 action and unique to the cartridge. The longer cartridge will pop off the rails sooner once you swap out the mag box to 30/06 length.
I had a 308 action that I turned into a 270. It fed like crap. Didn't like it at all.