Thanks David - v useful detail. Sounds as if you did it yourself?
I'm still havering about my own 411, needless to say. But my latest thoughts are that the GM200-4R that I was focussing earlier on has the same drawback as the Mopar transmissions in that the crossmember causes a big problem and needs modification.
I found this site
https://m.roadkillcustoms.com/automa...on-dimensions/ which gives dimensions for various transmissions (you have to scroll right to see the measurements) but it shows that the GM TH700-R4 has a trans mount in virtually the same distance from the block face as the TF727, and is 4" shorter overall. It's based on the medium-duty TH350 3-speed so should be no bigger, and possibly smaller width/depth than the TF727. (Am struggling to find info/dims for transmission case width and depth). There's the thickness of the adaptor plate to consider, but the same applies to any o/d auto fitted behind a 383, be it Chrysler , GM or anything else.
So am wondering if the 700-R4 tailshaft would fit over the top of the big round cross-member just like the TF does, plus a relatively simple mod to the mount. They have hydraulic controls, with upshifts controlled by a throttle-valve (TV) cable, which would need careful initial setting up and adjustment to get the pressure right - as do the rods on a Chrysler. It's GM, so readily available and relatively inexpensive. Same issues as any transmission re TC lockup - kits are available
But, unlike others on the forum, I haven't actually done anything about it....