T-10 First Gear Ratio

I have found a complete transmission that is out of a 1968 AMC.

the part number tag is 

3195689

AS2-T10V

I understand this is a 2:23 first gear trans.

and the Main case has 

T10P-1B

date code is:

I.8.68  (I believe it is an I and not a 1)

Any ideas what the date code means?

Some of you will recall from my recent Dyno Daze2 engine build that I have a hot street 401 with a bit of a ridiculous hydraulic roller cam destined for my otherwise stockish '70 AMX (3:54 rear, close ratio T-10) which is probably going to be a "challenging" to launch. I can throw more money at the problem and switch to a 5-speed tranny (and gain the OD 5th), but would prefer to explore mods to the T-10 first, as I intend to leave the car mostly stock and it is a hobby car not a daily driver of any sort.

From reading through the thread it sounds like upgrading my T-10 to a 2:64 or 2:43 its gear is still possible by spending some money at S&K speed? Anybody done this recently and know if the upgraded T-10 will withstand the 510HP/487 lb-ft motor? Or is there just a flat out better option such as an upgraded T-5 from somebody?

Nothing against this as an idea but the tranny costs how much?....and it requires me to buy a $800 bell housing, mess with the driveshaft I would assume, and probably the stock mechanical clutch linkage no longer works??

While building the motor I purchased an AMC clutch & pressure plate to go with the new flywheel, this is 10-spline stuff so all that would have to be changed also.

I want to hear about T-10 solutions! 

I get that the 26 spline input has more torque capability, but would assume it is shorter and thus requires the RM-8075 bell housing and probably some custom shifter work to get the new assembly to match the stock location. Plus the question if the stock Z-bar stuff is still workable. I don't mind swapping the clutch disc but was hoping to avoid the bellhousing and shifter monkey-motion.

Is the AMC input shaft the same as the Ford 10-spline? Looks like the same place has the Ford versions with the 2:64 first gear.

I will start poking at all this with some phone calls, maybe there is a tranny expert on the forum that can weigh in on these questions?