Automatic to 4 speed Conversion in '65 Formula S

There is a Commando 4-speed AND converted to slipyoke driveshaft for sale on FABO right now; check the want-ads.The commando has the 3.09 low, which with 3.23s will be a fabulous starter gear.
If your 273 is a low-rpm engine, then the od box could be a good option, otherwise I wouldn't recommend it, as the splits are quite far apart.
With a low-rpm engine(hi-torque), this ain't so bad. But when your cylinder pressure falls into the sub-130 range, AND you're hitting 4500-plus rpm, then pulling from 2400, with 3.23s being 33mph, acceleration is often measured with a sundial. The 2-3 is better, but 4500 in second is 63mph, so it ain't often that you get to use the 2-3 shift.
So yes you could change the rear-end out for say a 4.30 but that just moves the problem to a new roadspeed, and the starter gear becomes too large. So now your second gear is from 25 mph to 47mph, not particularly exciting as 95% of your city driving could be in that gear....... but ya-know; 4500 at 47mph is not a gear you want to be staying in very long. So at the shift, the Rs fall to 2670, and there you are back in the basement.
So I can't recommend that box for most guys; it sorta requires a hi-compression, hi-torque engine and or a light car.