/6 to np435 bellhousing
This seems to confirm that the Chrysler version of the NP435 is a bolt in swap behind a slant six.
http://www.sweptline.org/forums/viewtopic.php?f=19&t=22292
Of course as stated, you will need to make sure it has the correct input shaft spline count and diameter. The NP435 is pretty bulletproof and readily available for on the cheap. Good luck.