Automatic overdrive II

[T 20]

Hi guys,
I've got a '73 Dodge Van, B 200, w/ 318 & 727. I'm wanting to upgrade to an automatic overdrive. Can any one tell me which tranny will work for me? I've heard that a 42 RH, a 46 RH, and a 518 A might work. I won't be 'hot rodding' the ole girl, so, a medium duty tranny is all I need.
What I need to know is the year(s) and model(s) that will fit, so when I go to my local "Pic-n-Pull" junkyard I'll know what to look for. I'll (1) sniff the tranny juice and (2) pull the pan to see if there's any lumpy parts before I buy. I know that a little bit of fine, gray dust is OK.

I know I'll have to modify the driveshaft and tranny mount, that is not a problem for me. I also need to know about the configureation of the different tranny plug ins; which wire goes where (lockup converter,
overdrive, neutral saftey, and backup lights.)

Thank you for any info ya might have for me, I'd really appreciate yer responces,

Mo