If your engine has good low-rpm torque, (do a compression test) then the A8330d is a good option so long as you treat it as a 3+1 and go gently into overdrive.
The .73od will turn your 4.56s into 3.33s and 65= 2700 with 27" tires.,
This is a Cheap and easy solution ................. altho, your starter gear will be another 16% deeper going from; 2.66 to 3.09, making it a real short first gear, but Second will totally be worth it. Your current gear selection, in Roadgears, is;
12.13-8.75-6.38-4.56 /65= 3700..............With the od box you will get;
14.09-7.62-4.56-3.33 /65= 2700 ........................ Obviously that 14.09 is extremely steep.
as a streeter, I know that 6.5ish is an awesome gear, and all that you could ever want; unless you had a 6.80, lol. So, what can we do to give up that 14.08 and get something in the mid 6s for second; and I get 3.91s, for roadgears of
12.08-6.53-3.91-2.85 and 65= 2300 ................ compared to the current at
12.13-8.75-6.38-4.56 Thus your first gears are the same, but you loose the 8.75 in-between gear, in favor of that awesome 6.something Second gear, and you trade away the 4.56 gear for two other gears, namely 3.91 and 2.85.
When I did this going from 4.30s, I was very pleased. Mind you, I had a very hi-torque 367, which hardly balked at the 1>2 split. Your 340 may want to rev a lil higher in first, before the 1>2 shift.
Unless your car has some form of traction aid, the Dana is overkill,. I imagine you could trade it for a complete 8.75 rear with at least a3.91SG, AND the overdrive with it's matching BH. Maybe you can even get the swapee to throw in something else.
So you might be out NO money. and Still have the valuable standard box left. and something else you could use, like an organic street disc.
IMO, this is not the best solution, but it should be affordable, and easy, and quick.
NOW:
I highly recommend that you fabricate an OD Lock-out, cuz you are used to blasting thru 4 gears, and if you forget to be nice to overdrive, that will be the end of it. and maybe the entire trans goes with it. I would be remiss if I didn't tell you that I broke three of those .lol. But back in the day, I was buying them as cheap as $50. cuz nobody wanted to drag them home after the Swapmeet.
Whatever,
Happy Hotrodding