Sam
on my 83 D-150, I changed it to an instrument cluster from a 90 D-150,. The 90 cluster has an analogue speedo driven from a VSS, no speedo cable..
the standard motor products sc109t,
http://www.rockauto.com/catalog/moreinf ... cc=1084766
screwed directly on to the existing speedometer pinion drive housing on the 83 a833,,the 904 tranny uses the same speedo pinion drive housing. At least the ones I have seen in the local pull a parts do..
here is a e bay ad for one, I bet you can also get one from Brewers or Passon
http://www.ebay.com/itm/Mopar-Dodge-Ply ... 1371wt_718
I believe you will need the sc109t or alternative that matches the pulse needed by your electronic speedo.., the tranny speedo pinion drive housing, as well as a speedo gear that matches up to your axel / tire size.
the nice thing about going electronic on the speedo drive is from there it is ez to install a cruse control package,, as the cruse control can run off the same signal as the speedo.