Jeff,

The connector originally used on the 4P firewall is an Amp (Tyco) 206127-1.  According to the Amp spec sheet it's rated to 30PSI.  This is a bulkhead connector with male pins on both sides.  On one side of the firewall use an Amp 206125-1 mating plug and on the other side use an Amp 206126-1 plug.  Use Amp 205090-1 sockets to populate the plugs.  All of these parts are available from Aerocraft Parts (Lancair).  On the website they're listed under "Amp Connectors", not "Firewall Forward Connectors & Tooling".  Apparently some people are opting for the more expensive connectors listed in "Firewall Forward", even on non-pressurized planes, because they are more fire resistant than the Amp connectors. 

 

The Amp connector set provides 28 contacts through the firewall and you mentioned you need 31 so you'd have to use two of the Amp connectors.  I think the connector listed under Firewall Forward is an RMS connector.  I don't remember how many contacts are in it but RMS does make a variety of mil spec connectors and they do have a 31-pin configuration.  Check out http://www.pan-pac.com/products/viewCompany.php?company=rms.  Google also pointed me to www.introcorp.com/rms.html but I couldn't access this website.  Maybe they're down over the Easter weekend.

 

Tom Gourley