The only real upgrade is the lockup v6 tranny. Just the converter does nothing, as you have to have the right vavle body and the right trans case with the right oil passage to lock the converter. One other possible upgrade is better frictions in the tranny, but that requires a total rebuild.

I would use car-part.com and search junk yards in the US near the border that you could drive to and haul the tranny back. I don't think you would have a lot of trouble with customs duties on used auto parts.

I bet the linkage would swap, but you can also use an aftermarket floor cable shifter (Lokar or Art Carr or similar) to move the shifter and delete the sloppy column shifter. If you have a bench seat MM, the stock floor shifter may not work in any case, as it sits far aft and has always been an awkward move for long armed me...

I think most all the shifter bits bolt to the tranny/tcase adapter housing or to the tcase itself.

I used a 4cyl a/t behind a turbo motor and had no holding problems, and I suspect your tranny may be on it's last legs if it is slipping. You need to put a gauge on the line and regulated pressure taps and gauge tranny health.