1973-1990 dodge 1/2!ton 5 lug disc brakes. What is the diffrence in years and parts? What fits what, which caliper is easiest to get? Reason I'm asking is I found someone who would tackle the exspence and design of the dodge truck dropped spindle that a lot of folks want, but looking for an easy bolt in solution. If this works out, they would look into aftermarket pro-touring suspension conversions for 1962-1971 & 1972+ Dodge trucks. Any info or guides would be great.

American company?
I would say the 1984 model would be a good year,small bolt pattern wheels (5 on 4.5)plenty of choices.
New enough for parts availability.

I agree with using the '84 as your base sample. It still had 5x4.5" bolt pattern (for the older trucks) but used the larger outer bearing of the later trucks and Dakotas.
NOTE: It's late at night and my memory isn't what it used to be so corrections to my comments may need to be made.

Ok years interchage with each other? Is there specific reasons one year won't work/bolt onto other years? Or is the drop spindle market for dodge truck dead and should not try to do anything for truck suspensions?

Lots of people out there would like to have spindles for these!
The 72-93 trucks use the same spindle on 1/2 tons. the difference is the rotors. Later trucks have bigger bearing diameter rotors.
Yes the 84 is the year spindle that you should spec.
By no means is the market dead. Look on fb for 72-93 truck groups. There are several, and with huge memberships. One of the biggest issues with these trucks is the lack of readily available parts to drop them with. Suspension geometry gets crazy when you use drop pocket lower control arms, things get dangerous in a hurry when done wrong,with shorter springs, not to mention ride quality ummm suffers.

O.G.