Matching ceiling contour

[somefun]

I'm considering mounting "hockey puck" style halogen lights in the ceiling of my '74 Overlander. I'd probably install 8 or 10 in pairs, in the center panel of the ceiling, an inch or two from each center panel trim strip. The problem is, of course, that anything but dead center requires dealing with the ceiling contour. The lights that I've been looking at have a trim bezel that's plastic, that could possibly be trimmed to match the ceiling contour, so the lights would point straight down. My problem is:

1) How do determine the correct contour to cut.

2) Once that's figured out, how to cut that contour on the trim ring.

It's probably a far-fetched idea, but I know there has to be some "trick of the trade" to do this sort of thing. I work in a paper mill, and there's always contractors welding "Y's", etc. into stainless pipe runs. These require some pretty complex cuts in the pipe before they're welded. And they always seem to be perfect!

Any Ideas?

Thanks,
Curt