This is a stab at what class. In the PM you sent me I still didn't get enough info. I'm going to assume the car is a 2 dr cpe. If it's not that changes things. The 1970 Chevelle 2 DR Cpe has a NHRA factory shipping weight of 3372. That appears to be the heaviest small block in a 2 Dr Cpe. The 1966 300 HP 327 has a NHRA rated HP of 285 with the legal OE 291 casting head. According to the GT calculator the lightest class the car will fit in is GT/FA @ 3162.5 It will take 462 HP to run the index in that class and 613 to run 1 sec under. The heaviest class the combo can fit is GT/JA @ 3732.5 lbs. It will take 478.3 Hp to run the index & 626 to run 1 second under. The weight for those 2 classes includes the driver. The combo will fit GT/ G, H, I with the weight adjusted to fit those classes. Better check on those pistons. I'm not sure if the 300 hp 327 had 2 or 4 valve notches... A little CRS on my part. If I didn't miss any thing most of the other specs you gave me looked good. The carb on the 1966 300 HP 327 is listed as a Holley 3367A with throttle bores of 1.562 & venturi's of 1.25 and 1.313. You don't have to use the original part #, but have to use the correct bore sizes. It has to be built to SS legal specs. I hope I didn't screw anything up and this info helps you.
GT calculator
http://www.employees.org/~bhracing/g...ulator_1p1.xls