I'm new here so please bare with me, I'm doing my FIRST FRAME OFF on a 66 Chevelle, what books are the best for info on these cars for frame dims. for body mounts center to center locations, also plan replacing the whole cowl section (lots of rust) have never done this before and could use some help, Thanks Pat.

I recommend getting a hold of a Fisher Body manual for 1966. They are now available reproduction, and they will give you the measurments your are seeking.
Love your L72 '66 Belair!. I recall my old man passing one 30 years ago (man, I must be an old fart) in our '74 Canadian Biscayne at 90 mph (fastest I've ever seen him drive). It was a totally stock '66 BelAir 2-door in Danube Blue, whitewalls & wheel covers plus a Turbo-Jet 427. The car was near Stratford Ontario in 1975; I wonder if Pete Simpson (Mr. southern Ontario COPO) has ever seen the car since it as near where he lives. I love the big B-bodies from that era, especially the big block cars (we had a '66 Biscayne with a 250 six, the story of my life).