The parts you require from Merlin to fit the SPA-DG201B gauge kit are:
Extension Bolt 3/4" UNF M-EB-3/4UNF
Billet Sandwich plate M-TGASP200X.
Merlin have supplied several owners with these items in the past and the person who was there did know what was involved in fitting this gauge in a M3W, maybe they are no longer working there?
Lightspeeds installation is good but it is only for a pressure gauge not a pressure and temperature indicator as the SPA is. I don't think the temp sender would work at the end of a long dead end pipe, it needs to be located on the engine.
