I forgot about that Andrew! But there is a slight problem. The M35/37 air cooled trans was only used behind 199 and smaller sixes in big cars, 232 in the light weight postal Jeeps and early Hornet/Gremlin. They weren't used behind the V-8 at all.
The air cooled bell is very different from the radiator cooled models.
There may be bosses that can be drilled out for converting the M35 to radiator cooling. I know there are external pressure test points.
I had my transmission Brain Surgeon (Bill Burrage at B & E Trans, San Francisco) look at this when I had my current unit rebuilt back in 1989, he didn't think it was a good idea. It would affect pressures inside.
The air-cooled transmissions are FINE. Racing or hauling is probably a bad idea. They are light-duty but that is not the same as "junk".
It is CRITICAL to keep the throttle-position cable adjusted right, ALL OF THE TIME. It directly determines pressure on some band or clutch. It's not simply "kickdown" though it does that also. This the Brain Surgeon told me and said it's why people badmouth this trans -- they don't know to keep it adjusted right.
I get annual or biannual "tuneups", costs $100 or less, worth every dime.
Mine is starting to seep at the seals now, 16 years after last rebuild. Works fine still. Believe me, I use the hell out of this car, for a while commuting to Irvine from LA (2500 mi/mo), southwest desert driving, over 100 degrees, 200K miles of use on it in a Classic wagon. 300K on the car.