The the set up I want for my '68 122! The newly rebuilt B20 is ready, but John Parker says (last year):

There are a number of different Toyota trans that can be used. Generally in the US being from the rear drive Corolla, Celica and Supra ( except twin turbo ).
As some of these are quite old, there is an availability problem in many parts of the country - the same is true for parts. The one used in the Dellow kit for the ( W50?) is an old steel case trans, very heavy and with no greater power handling capacity than the M40/41. The T 50 is a much lighter, more modern trans but is harder to adpat as the bellhousing is the trans front bearing carrier, often modied and used in small racecars. The most popular, and most readily available in the US is the W55,56,57, and 58 series from the Supra (also some 2 WD trucks). This is the trans used in the Dellow kit for the 240.
Being a different shape than the T5 this trans may work better in a 122 than the T5 but other parts - throwout bearing, pilot, cutch disc - make the swap more complicated than the T5. We have can make adapter plates for it, but are not yet offering it and other parts to facilitate this swap into a 122 until we do a little more work.

Maybe I'll contact him to see if "a little more work" has been done yet.