At some point clean intake and block surfaces and mock up intake without gaskets to see if it's hitting the ventilator canister. They make diff. length canisters BUT looks like you already have the short one. Also take a good look at clearance between mating surfaces, intake should not bottom out on the ends of block leaving a gap at intake gasket sides. If still having problems swap a known good carb from one side to the other to rule in or out the carbs. Are those rubber or cork end gaskets on the block? Nobody I know of uses them anymore...……………………….