I bought the wrong transmission for my 66.

FYI
I took my overdrive long mainshaft to a machine shop, and had them make me a brass/bronze bushing for to accept a regular third gear.
Then I threw all the regular gears into an F-body alloy box, but used the od front synchronizer hub, then bolted on the B-body tail.
I already had the BIG-hole BH, so it was a bolt-in deal. I used the rearmost mounting pad, and fabricated an adapter plate to put the shifter where I wanted it and then just fabbed up some new tubular rods using cut-off bits from an old shifter set.


I happen to like my new further-back, raised, and moved to the left, shifter location. I installed a very short stick, Mr.Gasket BANG! shifter.

I got the bushing idea from, IIRC, the Ford top-loader, or maybe it was an old BW T-10, From the 70s, I forget.

The bushing hardly cost me anything.

All those regular gears will fit in a standard box with the small retainer, and then fit in a regular BH; all you need to do is to match the bearings to the bearing holes.

The long M/S only comes with 727-sized splines. In this way you should be able to reuse your $400 driveshaft.