I'm still undecided on whether to go .375 or .38-55. I'm probably overthinking it. After speaking with JES it seems the only difference in his rebores is the caliber stamp on the barrel.
When I was doing a search of .375 vs .38-55 I ran across this from Buffalo Bore

Here's part of it:
"Our 38-55 ammo is also designed to work in ALL 375 Winchester chambered rifles. ALL means ALL. Winchester, Savage, and Marlin all chambered rifles in 375 Winchester. All 375 Winchester rifles utilize chambers long enough to accept the 2.085 inch 38-55 brass, even though 375 Winchester brass is only 2.020 inches long. By using the longer 38-55 brass, we accomplish two things:

1. We get the bullet closer to the rifling’s and this creates a generally more accurate load.

2. The longer 38-55 brass, with thinner case walls than 375 Winchester brass, gives much more case capacity and this allows chamber pressures to drop immensely. i.e. our 38-55 loads give the same performance (a 250gr. bullet @ 2000 fps) as the original 375 Winchester loading, but at only 38,000 CUP instead of the industry max. pressure of 52,000 CUP that the original 375 Winchester was rated at."

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