I was wondering what this thread was all about until I read Sea Bass' post. My SAR-8 was one of the Greek imports and sure as heck doesn't have any aluminum receiver. Granted, it is distinguishable from the Original HK91, but not by much (Mag release, flash hider w/undrilled holes & screwed on so that the end of it is flush with the muzzle) That danged thumbhole stock was the first thing I ditched. The MSG-90 stock and PSG-1 grip are the way to go.
That all being said, My SAR-8 is, by and large, my favorite military style weapon that I have. Others being a pre-ban AR, Norinco AK (My dad's,) Springfield M1A, and a Garand. I've shot an '03 and an SMLE, and I still prefer the SAR-8. If you can't find/afford a real 91, go with the Greek/Springfield model. You can't lose.