Yes, I've loaded for a shot many old 7x57 Mauser rifles in various models. Most were 95 Mausers, and a few different makers. They did indeed use a long, heavy bullet, but that doesn't mean you have to reload with that same style bullet. The bullet can be set out a bit, if it shoots better seated closer to the rifling, but many shoot great with a small jump from case to rifling, and pressures are usually lower with this gap.
I'd get have the gun with me if I was loading for it, so you can set the depth better. Start by seating a bullet as far out as possible, and then keep seating it, and trying it in the chamber until the bolt closes, and all is well. You'll then know exactly how much free bore the chamber and rifling have, and where to start with loads.
I wouldn't load up a bunch of ammo without firing 5-10 first. Try whatever loads you prefer, and different bullet depths to see what the gun shoots best. Once you've figured out the bullet depth and charge his gun prefers, you can then load up as many as he needs.
Mine did very well with 140 grain jacketed bullets and 37.0 grs. of 4895 powder. That went across the chronograph around 2600 fps. I also cast and loaded with a gas checked 140 grain cast that I loaded with 19.0 grs. of 2400 for around 1800 fps. It too proved accurate, and good for deer sized game.
If his bore is good, and the gun is tight, it should be a fun shooter, and still serviceable for military matches, or deer sized game.