http://www.keltecweapons.com/The pictures that cycle through slowly, the one in the middle is an SU-16D with a few upgrades. doesn't look much like an SU-16 anymore.
Found the rail kit here:
http://www.redlionprecision.com/default.aspand the stock kit is available for less than 1 bill on Keltec's website..
I think I've found my piston driven, AR Mag fed, ultra-lightweight truck gun and hog killer

In a Charlie configuration, rather than the SBR. and I can probably piece it together for less than $1K