I did a few of the same things on my build, I started with a ‘74, /6 auto on the column and converted it over to a 340 4 speed, 8 3/4 etc. Should have the T56 conversion done by the end of the year (fingers crossed!).
I'll be watching! Keep tabs on how much work goes into installing a T56. Passon Performance is getting faster catching up with their A855 orders, but I hear there's still a bit of a waitlist