Used the Longshot stock by NIRODHA to find the butt sizing of the Longshot, so I could design a stock around it to replace the original one, namely a re-sized XZEUS stock.
Then I realised that I'm actually pretty okay with the longshot stock as it is. Figured someone might make use of this file.
Picture is of the dimensions, and a comparison of the longshot butt end vs. the XZEUS stock (not resized) and https://www.thingiverse.com/thing:2616467 by RayvenLover which I originally planned on using.