I don't know if it will fit, but Advance Adapters should know, and have an adapter if needed.

http://www.advanceadapters.com/

If it is only a direct drive transmission then I would see no reason to use it. I imagine that it does not have the shifter coming out of the top?
The sm420 is also a direct drive, has a great low gear for the times you want to use your truck like a truck, and bolts up with absolutely no problems. And has the shifter on top, like a real transmission should.

Why do you want to use the m20?

Grigg

•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
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"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-