I don't remember the last year of the 273. The only 727 that might work would be a small block 727, and if the 273 was 1968 or newer (crank pilot/converter issue).
I see so kinda the same issue, another solution I can think of (although might sound stupid), is to cut and swap the ends of the driveshafts so that way the 66’ shaft could accommodate the Ball and Trunnion tranny. Would that be possible?