V6 3 speed manual

Now you've gone from one extreme to the other; the 727 is way more trans than the 3.9 needs. And AFAIK you have to cut the tunnel to make it fit...., so if cutting, then you might as well put a 5 speed close-ratio in there, and at least make it fun.
AND here's why; consider the speed at which you will be doing most of your cruising. Say 32mph plus or minus a couple. At this speed, whatever it is, you will want a low-rpm cruiser gear to just tool around in. But you will also want to be able to downshift one gear and blast off.
With a 903 you might want 32mph to be 2400rpm and this will take 3.55s in the back to get about 32=2340rpm. So now you have a nice cruising gear.
Ok so how are you gonna downshift into low with no synchro and blast off? It can't be done in a timely fashion. Maybe it can't be done at all.
And 65=3000rpm with 25.5" tires
With the A230 close ratio; 2.95-1.49-1.00 ;32 might be 2000rpm with 3.23s, and 65will be ~2770. but now at least, you can downshift into first, and hit 4020 and blast off. Maybe you can even run 2.94s to cruise 32=1850, downshift to 3660, and cruise 65=2520
With the AX15 ,3.83-2.33-1.44-1.00-.79 and say 3.73s
You could be cruising 32 in third gear @2270 and downshift into second @3670 for blasting off with, and 65~2530.
And you can save that first gear for showing off, with a starter gear of 14.28 which might be 3.2 mph@600 rpm, a nice parade gear. Or you can lay rubber with it, powershift into second (8.69 ratio) and keep on spinning.
With the 727, 2.45-1.45-1.00...... you're gonna have to make some compromises. You just can't have it ALL; that is to say; spinning tires, a nice cruiser combo at 32 mph, and a low-rpm cruiser for fuel-economy.
Ok but, I chose 32 mph, cuz that's what I like to do. Maybe you don't care about that, IDK. so pick your poison and work it out for yourself; here is the formula;
mph= (rpm x Tire circumference)/ (1056 x rear gear x trans gear)

tire circumference is tire height x 3.1416; I estimated 80 inches in all calcs above, which is 25.5 tall.
Happy HotRodding