pretty much any aeg is possible to hpa, the question is how difficult it'll be to acheive.
a standard cylinder drop-in like the f2 would be the obvious choice, it'll come with either a v2 or v3 triggerboard but if the gun is doing something weird you can use a plugboard and wire in to the original trigger contacts.
the only other area will be nozzle length. you can either find one for a gun with a similar length, get a longer nozzle and machine it down yourself, or send the measurements to polarstar who can make custom nozzles to order.
there may be some fettling required- filing off stuff on the inside if it's catching on the gearbox, drilling holes for airline/cable routing etc.
i still hold the f2 is the best all-rounder engine on the market currently in terms of offering the level of tunability you'd want from the likes of a fusion engine, with the flexibility to be dropped into a much wider array of guns.