i belive the gmcs share carbs with 216s and early 235s. if you have a full pressure 235 ( with four bolts around the valve cover).
then the bols will be spaced out wider then your 228 zenith. so.. you can
1. get a carb for a 235,
2. ive heard of ppl fileing out the holes on the throttle body base, but i would want to ruin A good zenith.
3. swap manifolds. you need to get the stepped alignment rings. im assuming the 228 manifold fit fit you might want to investigate your self before going that route.
If i had the 228, id keep the carb to go with it, then find a 235 carb used for 60-80 bucks.
you'll need to fab a front mounting plate as well cause the 235 will be shorter.
