98 350 vortec, at idle pulls just under 12, just over 18 at higher rpms. what is normal specs for vacuum?

 

The actual spec isn't as important as the uniformity. Does the needle flutter at idle or under load or hard acceleration? A steady, set uniform needle movement at different driving conditions is much more important than the set spec.

Not that it's bad to keep your reading values in mind. Hopefully somebody else can provide you with an actual number.