Im not using a crossmember on my 63. No issues with it. You will like the T5 behind the Y.

Kenny  Onalaska, Texas

John, I don't think that a rear crossmember is required judging by the various transmissions that Ford hung off the back of the truck bellhousings.There were T-98 4 speeds and F-O-M's and Cruise-o's.
If you do decide to add a crossmember you should be able to leave the existing mounts and just support the tailshaft.

http://ford-y-block.com 

20 miles east of San Diego, 20 miles north of Mexico

I'm mocking up my '55 F100 which will have a Ted built y-block with John's heads and manifold when they become available. My question is can I hang the T5 off the back of the bell housing or do I need to add a transmission mount? I plan on using the original front mount which a single point mount and using the wide mounts on the bell housing. The original 3 speed transmission hung off the back of the bell housing but the transmission housing was made of cast iron. The T5 actually feels lighter but it has an aluminum case. If I need a transmission mount I think I would need to go with engine mounts on the sides which would interfere with the ram horns that I plan on using.

Thought?