Welcome to VAF!!!!
Nick, welcome to VAF
Good to have you aboard.
Are you looking for the seat belt mount points, or the shoulder harness mounts.
I would assume you mean the shoulder harness, due to the comments about paint, and headliner.
You really should have drilled them first, but you have probably figured that out.
If you can find another local 10 builder, you might be ahead of the game to go for a visit, and make a template------or at least take the measurements yourself------too many curved surfaces to be sure your method of measuring and someone elses are the same.
I see you are in Oregon, are you close to the factory-----???
Also, as the fuse top is a hand made unit, it is possible that the locations of the hard points may vary from unit to unit.
You might be able to find it with an electronic stud finder, the kind you use to find wooden studs in a finished wall. They appear to work on a difference in density.
Good luck------try a small pilot hole from the outside when you finally start drilling---easier to fix if you miss.