You can get the billet inermediate plate from,
http://www.californiamotorsports.net/
Thats where they are made. Plus, they have complete gear sets, billet side plates, billet bearing retainer, and other things to make your 901 or 915 stronger. Or any porsche transmission availible. Machining done in house. Got a built G50 with 40% lock and a cable shifter for a Ultima kit car for a client. Top notch, I use them exclusively for all V8 conversion transmissions.