Anyone know where to get a blueprint on the underfolder receiver?

Try this:

http://home.woh.rr.com/rnystrom/AK_underfolder_template.gif

I had the original underfolder template pic in my archives, so I redrew it.  I made it a little larger for clarity, but didn't change any of the dimensions.  It's been quite some time since I've actually done any engineering blueprint drawings, so I know I broke a few rules.  It should be good enough to get you going, though.

I HIGHLY recommend making a template of your specific parts and comparing them to the drawing before drilling any holes.  I hold a piece of paper on the side of the trunnion or stock tang and rub over the holes with the side of a pencil.  This method works really well for both pieces.  A Post-It is just about the right size and is self-adhesive.

The drawing just happens to work perfectly for my rear block with the original dimensions.  You may need to tweak a rivet hole location, but they should be damn close.

Thanks for the help!