069 & 163 are GM aluminum intakes for rectangle port heads and Im assuming you dont have since you have a cast iron intake. I would stick with what you have and swap the gear out for a 3.42 or 3.55 and that will help with gas mileage.. If you are dead set on swapping intake and carb just go with a edelbrock or weiand intake (aftermarket aluminum) with a 600cfm 4160 carb which will also help in mileage but you will loose top end but gain bottom end torque with a smaller carb..
Ok there's my $0.02
Holley (same as a Weiand. Same company) intake with 780 Holley and open element air cleaner with SS hood. No issues but I am not running insulation. For the record, my fathers 68 L78 insulation rubbed the air cleaner and eventually wore a hole in it so he pulled it because it would suck the insulation around the air cleaner at WOT.. I would venture to bet most if not all had the same issue when new or a year or 2 old.