Mitch, you may want to read up on sequential port fuel injection system and the Chevy 230/250 engine. Even fuel distribution may be an issue with the 1&2 and the 5&6 pairs of inlet valves. With the 1-5-3-6-2-4 ignition firing order, these pairs of Siamese ports due not have equal timing between opening sequences of the intake valves. Throttle body injection may be an alternative. Not to say there may be another work-around for a good functioning port injection system with the Siamese valve head. Later years of the Brazilian Chevy 250 had port fuel injection with a different cylinder head, using 6 individual intake ports

"greg64" at the following link initially installed port injection, then swapped in throttle body injection.
http://67-72chevytrucks.com/vboard/showthread.php?t=276823