LED housing assembly size

[Me_again]

Have a 06 Fleetwood flair, and wanted to change out the housing to LEDs. Doesn't make sense to sand down and refinish the headlight assembly since it provides such a poor vision at night anyways. I read changing out the bulbs is not as powerful as changing out the entire housing unit and since they're relatively cheap, why not change it out. so my question is: measuring my lights are 6x12, most leds housings are 4x6 or 5x7. For the people that changed them out, is there really a 4 to 5 inch gap? And as never doing this before: Are the brackets to attach them generally universal. or do I have to figure out how to mount them?

or plan B: refinish the headlights and use LED bulbs.

Thanks all !!!!!