Which trani did 65 valiant come with ? 4 spd

The 3.09 low has been taking everything my 367 can throw at it including a couple of 93 MPH Eighth mile runs. As said you just need a different tail and the large diameter mainshaft plus the appropriate rear bearing to marry them.
I like the 3.09 cuz it lets me run a 3.55 rear gear, takes off like it had 4.12s and still cruises at 65=2770 with 28s. The other ratios are about the same; HOWEVER, all the gears are different except IIRC the M/S lows are the same.
3.09-1.92-1.40-1.00 vs 2.66-1.91-1.39-1.00 ............... IIRC.

I have heard that some 2.66 boxes will not accept the 3.09 gearset without clearancing for the cluster. No big deal to solve with a die-grinder.
Your 340 will love that 3.09 box with up to 4.10s and 28s on the street. After that, first gear is a little short. I ran it with 4.30s and 27s for one summer, and that was too much for my 360; second gear came up awful quick. But, I did like the parade gear;600rpm =3.6mph.

I converted to a longshaft and moved my shifter back between the buckets, and up a lil, like a Viper. No more missed shifts since 2004.