First of all, if you are a lefty, you want the L, not the R nut.
If it's 43mm wide at the nut, that is 1-11/16" so the R2 at 1-5/8 is not what you want.
http://www.floydrose.com/nutsizes.html
Even with a 16" radius fingerboard, I'm guessing that the nut is actually a 10" radius since that's the most popular Floyd nut, but I'm not sure. Otherwise you will probably need nuts #8 or 10 as they are 15" radius.
So you are either going to need a L4, L8, or L10.
Your best bet is probably to email
floyd rose support and ask them.
techsupport@floydrose.com