68 T10

stick with the wide ratio trans I have had both and absolutely hate the close ratio like said second gear is useless if you want more get out of way power jump up in the rear end

Thank you for the responses. The five speed sounds like the way to go but I would like to keep the car stock. Just curious, what is involved in the conversion.

First off, finding a 2.64 or 2.43 first gear T-10 is not that easy. As another poster said, a decent, quality rebuild will run you at least $1000 for a T-10. Some will say it can be done cheaper. Yes, it can, but I said a 'quality' rebuild. Doing it twice is not very cost effective.
  Swapping a close ratio (2.23) T-10 for a wide ratio T-10 is as simple as unbolting one transmission and installing another, they are the same externally, including the shifter mounts. Of my 4 AMX's, I have 3.15, a 3.54, a 3.73 and a 4.10 rear axle ratios. All are 390's, some hotter than others, all have the 2.23 close ratio T-10. They differ widely as you might expect. The 3.15 is comparatively slow off the start, runs to 40MPH or so in 1st gear with no problem, but cruises at 65 at well under 3000 RPM. The 3.54 I haven't driven on the street, but it gets off the line much easier. The 3.73 car is a blast to drive around town, not so much on the highway as 65 MPH is approaching 4000 RPM. The 4.10 car is a drag car, not suitable for street use at all, unless you just want to make smoky burnouts in the first three gears!
  In the end, it's your call. I think the 3.54 rear end is a good compromise with the close ratio T-10. Rear ends are an easier swap than finding a good wide ratio transmission in my opinion. And don't forget, the reason the 2.23 is so widely used behind the 390's, the lower geared 2.43 and 2.64 wide ratio transmissions were deemed to weak to stand up to the torque of the 390's. The lower first gears on these units multiplied the available torque of the 390 to levels that were considered beyond the capability of the transmissions to reliably handle. Many on here will disagree, but AMC limited the wide ratio transmissions to the 290 and 343 engines in 68/69, only allowing the 2.23 close ratio behind the high torque 390's. I'm sure with moderate driving, a wide ratio box would survive a 390. Question is, can you drive your 390 moderately? I don't. What would be the point?

I think it's worth making a spreadsheet (I can give you one but there's lots out there) and spending time looking at RPM/MPH overlaps, aka shift points. The T5 I bougt from Modern Drive Lines has a sort-of close ratio, but the devil's in the details. 

Edited by tomj - Feb/23/2020 at 9:40pm

OK, lemme see if this works... this *should be* a link to a Google Sheets spreadsheet, for the current setup of my roadster. You should not be able to modify it, but you should be able to copy it and make your own copy.

Edited by tomj - Feb/23/2020 at 11:24pm