200R4 update
I have long felt the 200R4 was more desirable than the 700 to the point of installing one in my sister's '68 Camaro, but I also know unmodified examples of these transmissions are known to fail, even behind stock low horsepower 4.1 Cadillac grenades. You need to add aftermarket internals and valve bodies to give them any chance at a life, even behind a non high performance engine. At the very least they need a valve body from a Turbo Buick or Monte Carlo SS to shift properly.
When you add the need to modify the torsion bar crossmember to the expense of modifying and rebuilding the transmission to live behind any real torque and the cost of the adapter pieces, the decision for me in not choosing one for a Mopar A body becomes a no brainer. If I need to modify the torsion bar crossmember anyway, adding a little beef to a 518 that bolts directly to my motor is probably going to end up a far less expensive solution. Even installing a fairly new junkyard gen 3 Hemi and it's matching transmission might be in the same ballpark costwise as a building and installing a stroker LA and the 200R4 when everything all shakes out.
This thread has been a real eye opener, thanks for passing the information along, both good and bad, to help the rest of us.