Stick with the 86 and up. Yes there was a cooling upgrade. On second thought, go new, high output. A used one can fail at anytime and you'll have to do it all over again.
You are right on with costs. Bike, TCI,,,,,,,,, any you have just started. Tires, carb diaphrams, brakes, frame, fuel lines, slave cylinder, master cylinders, front forks,,,,,,,,. Best maybe count the costs before you sink with it.
Off hand, I have an 86 sitting here and have an issue with dealing with the cost to get it road ready.
That being said, here's some thoughts.
On the 84s, all of them, the frame has a rotting issue, about the middle of the bike. If you want something that is ride-able then check the frame out first. Some have been repaired, others hit the grave yard. This issue was remedied not until mid 85.
On the TCI, any 84 should work, if it works at all. You'll need to dig deep to get at it, but it is not impossible. Not sure is Ignitec (spell) still has replacements, @Skydoc might know better. Take out battery, battery floor and proceed from there. You might get lucky just cleaning the connector, but I doubt it. It's a bit of work. When you get it out it can be opened and that might give you a chance to clean and repair. It has been done before.
Starter is normally weak, but if the engine starts promptly then does decent service. Most have gone with a 4 brush 2nd gen unit.
There is a relay that governs the fuel pump, so it will shut off, either due to pressure or time.
Best of luck to yah, post more if needed.
Yep, I cab just tell, not so hard really, just look at them their pictures and yah can see the lips moving in the same direction they always have. More tall tales than a mountain of golf balls. Wished I could have been there, I could sell all those balls.
We would need to what kind of kit it is first of all, but seeing as all 86 to 91 frames are the same, it should fit with the same ,if any, modifications.
During our retirement we have been inundated with requests for assistance of one type or another, so now we have moved to an unknown location, so when I find it back I will let you know.