I recently bought two of the RIA/Armscor guns, for the purpose of recreating WW2 GI .45's (I already had the GI slides and barrels). So I was primarily interested in the RIA frames.
The good news is that the RIA frames will accept GI parts with no problem. The bad news is that nearly all of the RIA parts have significant differences from the equivalent GI parts. (These remarks apply to the basic parkerized RIA gun.)
-- Frame -- close, except that the RIA has a chamfered magazine well.
-- Slide -- the RIA slide has an enlarged ejection port, and taller sights. Not a problem for a shooter, but visibly not authentic for a WW2 gun.
-- Mainspring housing -- flat, grooved, and with no lanyard ring. Not GI.
-- Trigger -- long, and grooved. Not GI.
-- Hammer -- clunky profile. Not to be confused with a GI hammer.
-- Grip safety -- does not resemble the GI part. The tang is too long, even in comparison with the "long" GI grip safety. There is also a strange internal difference.
-- Grips -- the RIA gun has very thick, smooth-surfaced wooden grips. (Made of some Oriental wood. Certainly not walnut.) No resemblance to GI grips.
-- Thumb safety -- late type. Not correct for a WW2 gun.
-- Recoil spring plug -- the knurling is too coarse, and crude. Not dimpled for spring retention.
-- Ejector -- postwar, aftermarket type.
-- Sear and disconnector -- visibly delicate castings, as compared to the more robust GI parts.
-- Magazine -- not a GI-type magazine.
The parts of the RIA gun that are usable in making a true GI clone are: the springs and pins, grip screws and bushings, magazine catch, slide stop, recoil spring guide, and barrel bushing.
Bottom line: If you want to make a true GI clone out of an RIA/Armscor "clone," figure on at least doubling the price. (Still much cheaper than an actual GI gun in equivalent condition.)
At the last gun show I went to, I saw a (used) Auto Ordnance/Kahr Arms .45 clone that was much closer to a GI-issue WW2 gun. And the price was only a little higher than an RIA gun. But these Kahr guns don't seem to be as available as the RIA guns.