V6 3 speed manual

The A903 3 speed is non-synchronized first gear unit with very small ancient-technology synchros that are light-duty,slow-shifting,with ratios to match the original engine.You know downshifting into first is gonna be a pita,right.If you spend all the time and money to install it, and then blow it up, what's your back-up plan? If you keep it, I recommend to buy a spare trans asap and a source for new brass rings.
If you just gotta have a 3 speed, I recommend the A230 with a floorshift. It is fully synchro'ed and shifts easier and faster, and the V6 will never break it. And the bonus is that it bolts right onto the 318/340 68 up bellhouse. You will need a new driveshaft.
But if I was going V6, I would bolt on an AX15 5 speed with ratios of; 3.83-2.33-1.44-1.00-.79od..This will work well with 2.76s to 3.23s
The A230 has either; close-ratio 2.55-1.49-1.00 or a wide-ratio of 3.08-1.70-1.00
As to the 903 ratios;I don't recall them; maybe around 2.95-1.54-1.00; I'm guessing.