I have two boxes of .350G&H - one is unopened!

For comparison, I lined up a .375H&H, .350G&H, and a .300H&H.
All are the same length, base diameter, case diameter, etc.
The only difference I could see is the belt width was a little greater on the .350 and the .300 compared to the .375 - perhaps a difference in manufacturer - the .300 is Winchester, and the .375 is Western.

Add to this a .333G&H Super Mag. and a .275H&H and you have quite a versatile group from the same parent case.