Buy a Macs header that fits the 40LA. Get a mousse can that measures 1.75" diameter by 6.5" long. And get a few inches of 1/4" inside diameter tubing (aluminum, brass, copper, etc.) You'll also need a package of JB Weld epoxy (not the 5 minute JB Weld).

Build the MCP according to Bob Adkins' instructions at:
http://webpages.charter.net/rcfu/ConstGuide/MCM.html

For an Avistar, use an APC 10x5 prop on your 40LA w/MCP and prepare to be amazed!