AFAIK, no vacuum line on any A-body from 1967 to 1980 ever had a clamp on it, NOR were they covered in a mesh thingy. Vacuum lines for the booster and the PCV are thickwall offerings to withstand the vacuum.
But, service manuals are often false, or too much generic.
You're probably right. Vacuum hoses don't really need clamps.
I will also change the hose for a non fabric covered one.