Nut radius question

I'm putting together a pinepartscaster with my daughter and trying to figure out what to do about the pesky nut. The nut slot on the neck we have is 1/8 inch wide and 1 11/16 long and flat on the bottom. The fingerboard radius is (apologies to vintage spec lovers) 12". The Graphtec website has strat-style Tusq nuts that are the right width, length, have the right string spacing and flat on the bottom. But the top radius of the nut looks much smaller than the radius of our fretboard. Most places I've looked don't seem to have pre-shaped nuts for a 12" radius. Or they are a mile wide for Gibson guitars.

I assume this is bad. Do I have to get a blank and try to shape it myself (and then give up in frustration, get a new blank and have a local luthier make it for me)?

I'm new to the forum and to putting a guitar together and I'm slowly learning a lot. Thanks for all your help.

Get the slotted nut and radius it to suit your guitar. It won't take much.

Do I have to get a blank and try to shape it myself ? yes, or pay somebody else to do it ...

You'll get the correct radius when you set the string height at the nut, then you can shape the top to match. Any nut you get will require some work so this is a good chance to learn something new.

Shaping a nut is quite fun and rewarding. Bone is pretty hard and it's difficult to mess up unless you are using large powertools. Check out some threads that use the "flattened pencil" as a fret radius and nut height guide.