Just have the transmission shop convert it - early bell housing, input drum and pump cover/stator (The pump body didn't change between those years) need to be installed in place of the the later style ones that are installed into it now. Ask the transmission builder if he'd take the non-conforming parts in trade for the ones that you need...I do these conversions all the time based on what parts i have on the shelf and what is required to make something work and usually work things out w/customers or whomever if it makes sense for both parties.
Should be some addl labor to do the re-work but the 300mm stator-style input drums are worth a lot more than the early style like the one you need so there should be a bit of offset in your favor there. Same for the pump cover/stator assembly. You'll need to purchase a correct torque converter but perhaps he'll also accept the new TMBX as partial trade as well.
Situation was as I initially thought it was but glad was able to confirm it.
Good luck w/it - hope you can work it out.
