I know that the 98 magazine boxes were a little different for different cartridges. My question is; Does the magazine box need to be changed when rebarreling from the standard 8x57 to .30'06, .270, or .35 Whelen to feed correctly? Will the follower have to be changed? Thanks.

The magazine is plenty wide enough for those cartridges but not long enough. However, it is easy to make them long enough; often a few minutes with a file is all it takes.

My 9.3x62 feeds fine in a standard military 98 box. To gain a little length in the magazine, take a good file and square off the "fillet" in the magazine's inside corners on the cartridge base end.