Most available sets are generic.... one size bushing fits all locations. Ground Up @ www.ss396.com offers a decent set with flanged head bolts. If you want original sized bushings, you'll have to buy some individual bushings from CARS or Restoration Specialties.
Ground up for conv, you get extra needed for Buick. and Restoration Spec for solids and Cars, or Restoration Spec for core support, depending on style.
I know this is a little old but i'm at the same point. I got the generic 64-67 A-Body from inline tube. There generic but bolts are correct. My core support is same a 67 chevelle so i see many placed have these. looks like Restoration Specialties have the solid ones but mine are ok. Mounts 1,2,3 and 6 are more difficult to find. any luck with these. 1&2 same and could use from generic set. 3 is smaller diameter hole into frame and larger outside diameter. 6 again i could use generic ones as they are pretty close. Any luck from others?