So quick update:
After talking with a few converter experts that know MoPars from all over the country- I found out the reason no such converter is available is the diameter of the input shaft for the 68’ and up 27 spline 904 is too big for the inside converter bushing inside that nub (or register) so either the input shaft has to be machine down at the end or only a smaller input shaft from a 67 and older 18 spline can be used. The engine machine shop kinda screwed me with not doing as i asked and opening up that register at the back of the crankshaft when building the 273 in the name of strength. So the update is the original 66’ a-904 is being built at a local shop and they are going in and rebuilding the converter and changing the stall on the 66’ small nub converter. They have done a few transmissions for me and have a complete in house shop dedicated to just converter building. I was amazed when they showed me the converters they produce - I did not think such a shop was available on the East cost. And just 30mins up the highway for me. They did a 66re for me about 2 months ago and said “they rebuild converters in house” but had no idea the level available. They are also car guys and understood my situation.
So that in a nut shell is where I am at. If you have a small register or “nub” crank shaft you are limited to either machine it larger on the crank end OR you are stuck with major torque converter rework to make a auto work. As of this writing I could not find a company that makes a proper spacer to adapt down the nub of a 68’ and newer convert to a small nub 67’ and older crank with a bell housing spacer to allow for the needed extra room.
273= $$$$