My "USA" body has a "C" of 16.5mm and a "D" of 20mm.
My RG450 seems to have a "C" of 16mm and a "D" of 20mm. (kinda looks like 15mm in the photo, but i double checked and its 16mm.)
The neck seems to be 17mm up until the fretboard hang.
The whole neck measures at 25mm, without the frets.
I didn't disassemble my RG560, but it seems like the neck is also around 25mm.
The weird part is that the "D" on the RG560 seems to be around 19mm?
EDIT: just assembled the 450 and it also reads 19mm from the same place, so this means this isn't a reliable way to measure it at all. Please disregard this one. But probably the 560 is also 20mm, not confirmed.
Could it be that they had different body sizes, and maybe even different neck sizes?
I'm even more confused now than when I started all this!
Edit2: might be worth to add, my 560 is from 1987, my 450 from 1993 and my "USA" body I got no clue at all.