HC on page 321 of the manual of cartridge conversion there is the .41 Jurras. it is a 1.298 long necked down cut down 30-06 case. it does in fact have a neck. its what I have in mind but longer to fit in the ak mag.Now I'm interested in how you would shoulder the .44 GS to a .41 - is there enough there for a neck?
on page 286 there is the .375/38-40 another cut down 06 shell it is 1.125 long
on pg 282 there is the .375 shanon same thing but 1.315 long
I think all that it would take to make this is the correct set of custom dies.
some of these would fill the same void that your 9x39 would