How are the 2 piece colt mag blocks? I am considering drilling and pinning a 9mm lower with a 2 piece set, and wanted to see if it was worth the hassle and money saved. ( I can get a 2 piece set for less than $40) Do the blocks float on the pins, or are they solid.  Also, if someone could provide me with a template for the pin holes or a good picture, I would greatly appreciate it.

The Colt blocks (2 piece) are held in place via the roll pins, no floating.  I do not know if there is a given dimension for locating via "X" and "Y" axis, unless a friendly can measure for you and provide the correct locations.

You would be best served using an ASA or Garrison block that drops in from the top, then you are free to remove and swap upper to 556 on a moments notice, and be firing other caliber in maybe 30 seconds --- give/take a few seconds.

You might try Bryan Pritchard in Marietta GA, as he has handled a bunch of LE 635 subs for parts kits, or Dave Hineline (find him in the M16 forums.

Where can you get a colt two-piece set for less than $40?  I can't seem to find them anywhere, or am I looking in all the wrong places?

J

No real call for them on a non-Colt factory built gun, current market is 1 piece, even from Colt, which ASA/RRA/Garrison copy for the most, but the ASA and maybe Garrison being a drop-in from the top. Colt uses the 2 piece on their factory 9mm SMG, and older factory 9mm AR-15.

Once in a great while a set pops up, best to place a few "WTB" on  some of the various boards.