Yep, Travis at WAR is who you want to talk to about this level of Prod modifications.
Given the level of modification and cal, might also consider building one from a 25 cal Mrod. There are few projects found on the web doing so. Lloyd made a double tube version for Manny. If I was to make a 25 cal pistol, would use a Mrod based one. While I'd like the left hand cocking of a Gen II, don't think that can marry up to a Prod pistol grip frame.
Both involve a decent amount of modification, so need to research if there are other guns that can be had out of the box. My total guess on cost is $750 - $1000.
IMO: the Prod makes for a large pistol, ie like at 1800's dueling pistol, but since you want 25 cal, you want all the air you can get. Myself, I went with the slightly smaller size of the 1701 airtube. Makes it about the same size as a 1377. It is still a large pistol.
So, basically a Prod with 1701P airtube, cut down barrel and shroud. The shroud provides little sound abatement, but keeps the iron sights high enough to see over the mag. BSB, 110 tp and heavier hammer spring gives 16 shots @ 16FPE w/JSB 18.1g. You can get 24 shots given the close range of 25yds or less with iron sights.