so will any mauser 98 firing pin work in the 08/34.30 and what size barrel will work
"Most" Model 98 firing pins will work, but again, there are minor differences that may cause problems.
Most Model 98 Mauser's used the same barrel threads, but again, there are some exceptions.
Bottom line is, you have to know something about the various Model 98 actions.
If you intend to have a Mauser re-barreled to a cartridge not original to your specific model, you have to do some research to figure out what cartridges are compatible with that action.
As example, most rifles will need work on the magazine box and possibly feed ramp to allow using the longer 30-06 cartridge but usually work okay as-is with the .308