This feels weird, yet strangely good

[Patrick Chadwick]

First, the book you really, really need to get is "Backbone of the Wehrmacht" by Richard D. Law.
From which you could learn that 243 was the manufacturer's code number for Mauser-Werke, Borsigwalde.

The laminated stocks were indeed made from beech. Either a beech-laminated or full walnut stock is acceptable for the period. I doubt that the sporterized stock you have there was ever the original stock, as it looks as if the bolt-take-down ring was never fitted and the cut-out for the sling attachment is also incomplete. My guess: it was an unfinished stock that was sporterized.

The simplest way to get all the parts you need is to look for a wallhanger as a parts donor. You would probably be able to get everything as individual parts, in time, but the cost would be considerable.