Peter, I bought my adapter from Castleauto part no GENIII-T/S 0354721442
http://www.castleauto.com.au/contact.html
I also think Howard Instruments where I got my VDO guages and senders from sells these adapters as well. part 320.054 M14 x 1.5 to 1/8" - 27 NPTF 20mm 0394574755
Peter, I dont believe there is an electrolysis problem - there was some discoussion about this a while back. I am pretty sure some of the existing senders on the Engine are Brass.
Rgds
Gregg