I have a 1967 Newport that I want to buy a gear vendors overdrive for and then regear the rear end. They only offer one o/d ratio and going by their charts it appears a 3.55 would be returned to the factory 2.76 ratio, and a 3.73 would result in a 2.98 and a 4.10 would result in a 3.23. I wonder if I can get by with the 4.10/3.23 rear end and still be street able on the interstate, or would I spin the motor at too high of an rpm? I am told that you could option the old Chryslers with a 3.23 from the factory? Is that true? Does that mean I'd be perfectly safe at that ratio to cruise 70-80mph down the interstate? Would I potentially be a lot happier with a 2.98 rear end. I feel like the 2.76 just lacks a little grunt in third gear and maybe 2.98 would give me just the little extra I want, and the 3.73 would give me lots of grunt if I ever made it to the strip?

Greg -

I ran 3.23s for decades in my Charger with no problems on the highway or track.
The 4.10/3.23 with the gear vendors od should be perfect.

Archer

does it make the engine spin pretty fast on the interstate, like uncomfortably, or possibly that would all be a matter of taste?

Another question, is it better to get a gear vendors or a transmission swap? I lean towards the gear vendors because I won't do the work myself on that part of my build, and it seems simpler, less custom fabrication etc...

Greg -

Kinda depends on how fast you're going and your engine's power band.

Plug the numbers into a gear ratio calculator and see if you like the results or not.
https://purperformance.com/p-29669-rpm-calculator.html

Right now I'm happy with 3.90s, w/o OD, but that me, and my motor isn't stock.

I like the GV stuff, I think it's a great idea, but it does have limitations, like low speed driving in OD (aka oops mode).
They do have a new servo mode that handles that, but I still prefer the older "switch on/switch off" set up.

I may go to one later on, but right now, kinda happy with were I am.
If you want the GV rig, it's a great set up, OR you could just go any where from 3.23s to 3.73 w/o OD and be done with it.

Archer

I've looked at that. My motor is stock for now, but eventually I want to rebuild it with a hydraulic roller cam, heads, and efi. Eventually..... I like how my old 66 cruised with 2.76 gears and I liked the response when I kicked it down into 2nd but hated how it fell off when it wound second out. So if I go to a 4.10 and get a 3.23 result in o/d it may be unpleasant for me, but if the motor genuinely doesn't mind, it's not a big deal. But 3.73 might be perfect, cause 2.98 might be the perfect solution to my third gear and then I basically gain an extra low gear to get out of the hole a lot quicker.