What cam?

You can measue there height and width unsprung as well as wire diameter. But the true measure of the spring will be in the amount of pounds the spring is at there installed height and near coil bind.
I'm not exactly sure were the best place to get a reading is.
Oerhaps an engine builder or racer would know this better.

The problem with this mystery spring is it could have to much pressure on the cam and wipe it out.
Not enuff and you would have valves floating. (Poor RPM ceiling)