Just got a batch of GF Nylon prototypes in, and if they're good, next step is 6061. That said, these are for sale! They mount to a CCI stock class body, and take an Empire spec feedneck (or spring feed).
$10 each, shipping included. You'll need a button head, 8-32 x 1/4" screw to install.
$10 each, shipping included. You'll need a button head, 8-32 x 1/4" screw to install.