How bad are the head lights?
Very bad. They are cheap, nasty, poorly-focused items that take the intrinsically bad 9004 (HB1) bulb. And the circuitry is underspecified, so even those weak bulbs are underfed. That part's easy to fix with a
relay kit, and you can improve on the bulb situation somewhat by installing the best available 9004s (
GE Night Hawk Platinum 9004NHP), and of course you should make sure the lamps are correctly aimed. But if you need more than that, and you very well might, then you'd need to look at installing auxiliary lamps.
There is no safe, effective, legal way to put a "Xenon" (HID) light source, or any other light source that is not a 9004 bulb, in those headlamps.
I believe they share lights with the 91-96 caprice.
No, you're thinking of the Oldsmobile Custom Cruiser. The Buick Roadmaster had its own headlamps not used on any other vehicle.
Is there a housing upgrade available, possibly from an overseas market roadmaster?
No. The Caprice was exported, but not the Roadmaster. There used to be UN-spec headlamps for the Caprice, with H4 bulbs and glass lenses, but they were discontinued years ago and have been unavailable for quite some time -- and they would not fit a Roadmaster.
