Here's the link to Flat-O-Matic who makes an adapter for the C4 to the Y.http://www.flat-o.com/carproducts/yblock.htm
I've seen this particular adapter in the early 'Birds. Checking in the Y-Block Magazine will get you some other companies making adapters for the overdrive transmissions and allowing them to fit up to the Y. Searching both this forum and the old forum will likely produce the names of these companies also.