O.d.

so looks as the early a body gears are the best with a gv for a 340 duster or an early 340'd barracuda .

I can't say that, as much as I'd like to.
First the GV is a big investment.
Second,when you hang it off the back, it messes with the driveshaft angles and with my lowered car, I've never been able to get rid of that tiny bit of vibration.
Third;And the big one is this; It comes with a little computer, and a really ugly-for-a-car shifter switch. The computer's primary job seems to be to prevent you from engaging OD in reverse. Secondly, it likes to delay the shift until it thinks you have enough driveshaft speed to build enough oil pressure to engage with a minimum amount of slippage. So if you are running small gears, you will need some speed before it engages.
Ok for most guys this is a good thing. But if you are gonna split gears at full throttle, we can't be hanging around waiting for that slowpoke ECU! So I bypassed that baby. I mounted a push-on/push-off switch into my shiftball, and wired that shift solenoid direct. What I discovered was that unit shifts like lightning, wired this way.I kid you not, the tires never stop spinning at the shift. So this is good news right? Not so fast; remember the primary purpose? I discovered that the Solenoid can easily hold pressure during an entire traffic-light change, allowing you to move forward in any O/D gear you might have rolled in on.Unfortunately, this same feature works on the parking lot and if you forget to outshift and put it in reverse, you will almost immediately kill that badboy! It doesn't take but two feet, and it is smoked! And the GV people charge 1/2 the cost of new to repair it. It's a flat fee, and non-negotiable.So you better figure out a way to prevent that from happening.And when operated directly like this and the clutch is locked up, it will rip 340 disc springcarriers up and spit out springs real quick.I was running a CFII for a while, which takes the abuse, but man that thing is harsh.
Fourth. It requires a special expensive oil, and it doesn't remain leakfree forever.And if you operate it at too low an oil level, you will be rebuilding it again!
Fifth;If you want to transfer it to another different type transmission, you will have to send your current adapter back, and wait for the new one to arrive, cuz they absolutely will not sell you an adapter, without receiving back an adapter.
If I had it to do over, Idunno. I think I might spend a little more and get a 5 speed. :(
I know if the McLeod was available today, I would probably buy that, instead.Probably, maybe...