Very good find and purchase buckstix. Getting all those new cases let alone the bullets is a heaven sent as 10.75 components are not always easy to come by.
My own 404 started life as a 10.75x68 only as a Type A Pattern No.1 and with serial no 109624 it was made in same 1930-31 year range as yours.

I have a few of the original early RWS 347gr bullets to hand that were made for the 10.75x68 and a couple of old rounds, one a Kynoch with a solid bullet and the other a Berdan primed case that had an odd 285gr Hollow Point bullet seated in it. I pulled the bullet to ascertain it's weight and found there was no powder in what I thought was a loaded round but it has the original unfired Berdan primer. This cartridge was given to me years ago by a friend so I don't know how it came to be as it was with a strange case, Berdan primer and bullet.

RWS 347gr bullets for the Mauser 10.75x68.

L - RWS 285gr .423 HP bullet. R - RWS 347gr SFP .423 bullet

Unusual 10.75x68 Berdan primed case which had the RWS 285gr HP bullet seated.

Will be keen to see how your new toy shoots.