I was wanting to swap over to the 91-92 style flip up headlights on my 85 but I heard that it's impossible to do?? Why is that?

I know they have there difference "smaller bulb, different plastic housing." but thats why I want to swap over.

If someone can explain why I cant do the swap that would be great.

 

the motors are the problem they have different connectors.

 

Yeah, the motors and relay setup differ. The 82-86 used three relays, and three-wire motors while the 87-92 used a single relay box, and two-wire motors.
You could retain your original motors and wiring and (I think) the basic mechanism is the same, and just swap out the buckets that the bulbs mount into, along with the trim.
The trim would look out of place on an 82-90 'bird, as it doesn't have the shape to fit the 'indent' of the earlier nose piece because the 91-92 is designed to fit flush.

 

but it will sit flush....

thats all I needed to know, i'll just swap motors.

 

just swap the motors is all you need to do