If you’re not averse to going with a single DIN unit, then that’s actually going to be the easiest course of action. A single DIN is about an inch thinner than 1.5 DIN and even with that reduced dimension, the face plate for a single DIN head unit just barely fits into a stock bezel (the lower right hand corner is right up against the bezel's raised relief). And that is with some very careful modifications to the bezel using a 32 TPI hacksaw blade, a utility knife and a file for dialing in the final opening dimension.
Modifying the actual steel dash board isn't as critical - because the bezel hides everything (BTW - the increased opening is best made with a high speed cut off tool. Tried the first time with a Sawzall and a fine tooth metal blade - it was a nightmare). But even with the bezel hiding some mistakes, the enlarged opening in the dash must be carefully positioned/located. This is primarily so that at final assembly, the mounting sleeve will allow the HU (and it's faceplate) to fit into that lower RH corner of the bezel.
Also, the steel of the dash is raised and contoured in the area around the radio. A single DIN measures about 7 1/8" X 2". A DIN and a half, on the other hand, has the same width but is about about 3 1/4" tall. If you want the small flange on the front of the sleeve to sit flush with the steel dash, you will want to be sure the opening does not extend into the raised areas around the edges.
I am not very articulate tonight. Below are some pictures that might help explain what I mean.
A stock, unmodified dash board:
You must be registered for see images attach
You must be registered for see images attach
You must be registered for see images attach
You must be registered for see images attach
My first attempt at modifying a steel dash to accept a single DIN sleeve (not my best work I admit, but it wasn't a show truck - I just wanted a radio):
You must be registered for see images attach
You must be registered for see images attach
You must be registered for see images attach
You must be registered for see images attach
You must be registered for see images attach
An unaltered dash bezel (sorry, I couldn't find any pictures of one I had modified):
You must be registered for see images attach
You must be registered for see images attach
What a single DIN looks like when mounted (note how close the face plate comes to the edge of the bezel):
You must be registered for see images attach
You must be registered for see images attach
You must be registered for see images attach
You must be registered for see images attach
I am not sure how practical it would be to attempt to fit a bezel from a different style/model year truck on your 1984 dashboard. I imagine there would be some serious issues just with mounting it to the dash itself - not to mention fitment with the instrument panel, steering column, climate control panel, dash pad, etc.