I studied this for a long time before I decided to cut those holes. On mine I used '39 taillights because that's mostly what they used in the '40's and that was the era I was building. I have hundreds of photos of '32 Fords from the '30's-'50's I've copied from the early dry lake's racers. My dad like the look of the ones I did on my Brookville body, so he had me put them on his original '32 roadster. It about killed me drilling those holes in an original roadster. The guy up the street liked the look too so I cut the holes in his Brookville roadster too. I don't mind cutting a repro body, but my dad's original body was hard thing for me to do.
Probably more than ten-years years ago I went on mission to the LA Roadster Show looking at rear lights and license plates and I decided The SoCal Speed Shop's '32 Roadster's layout looked the best. One thing though is it did not have a license plate light because that would have cluttered the look. I took measurements off of it everything. Out in the swap meet area there was a NOS '39 rear fender for sale so I made a template from its light hole. I figured I might as well cut the hole using an original hole pattern. One thing I noticed is the reproduction '39 taillights mounting studs are not all mounted exactly in the same spots. They were probably hand drilled and they didn't get the studs in exactly the correct spots. The screw that holds the lens is not drilled in the same spot either between the two lights. It wouldn't matter mounted on a fender, but those lights need to hang exactly the same height on either side of the license plate. Something to check before you drill the holes.
I put my license plate and the '39 lights on a copy machine and made a paper copy of them that I could cutout and tape to the panel and then stare at it for hours. I decided SoCal Speed Shop's layout was pretty good; except like I said they didn't have any rear license plate light and that bothered me. It gets a little crowded to mount the light above the license plate, you could go with one light each side of the plate but that clutters it up too. I finally came up with my own idea. I welded a plate to the rear spreader bar to mount a club plaque on, which I was going to do anyway. On the back side of that plate, facing backwards, I mounted the license plate light, so it shines up on the plate. You don't see it because it's behind the club plaque. I ran the wire to it thought the rear spreader bar with grommets so it real clean looking. I just need to finish the car; I get sidetracked on other projects.