Morning John,
These are the very same guns I'm working on at present. I've stripped both stocks back to bare wood. In the case of the 50T01 the varnish is particularly obstinate.
There does appear to be two different sizes on your guns like mine. The 50 I'm working on is a .177 example and I'm sure the .22 example I have has the wide shoulder part on the outside. I'll double check and what I think could be enlightening could be the respective dates.
The reason I say this is I can't see Diana starting out production the easier way and drilling the widest part of the bushings on the outside and then deciding to make life difficult for themselves by swapping to drilling it from inside. There is not a great deal of room inside the inletting for the trigger and indeed it's a fiddly job putting the bushes back in place ready for reassembly.
I've tried to get inlay panels for this 45J too but they are simply not available nowadays.
I'm going to think of something to put in there as an alternative soon.
Best regards
Dave