Automatic Transmission - GM?

The 456's spiritual ancestor, the 400/400i/412 DID use the GM built TH400 transmission(only) but not the 456. It is Ferrari branded but they had help designing from specialists in the US, not GM. It is a transaxle and bears no resemblance to anything from a C4 Corvette which uses discrete gear box and differentials.

 

Jason- The 456 and 456M transmission was based on a GM design, but very heavily modified. Not the same as the Corvette automatic.

 

I think ZF ?

 

A gentleman named Adrian Turner ran the business unit of Ricardo that codesigned/built these transmissions, loosely based on the GM 4T80E. Afterward, he ran a business in the UK repairing/rebuilding these, however it appears he's no longer with us as his webpage no longer exists and his email bounces. After further searching, I found an obituary for someone of the same name from the same town who passed in 2011. I assume they were one & the same Adrian Turner.

Mr. Turner only made 3 posts here, and each one had good information. It's a pity he and his expertise are no longer with us:

http://www.ferrarichat.com/forum/138534502-post5.html

http://www.ferrarichat.com/forum/138596213-post28.html

http://www.ferrarichat.com/forum/139261710-post135.html