[Eljaro]

If you use some type of 10mm thick phenolic spacer (which you should in order to keep the heat from creeping up to the carbs and boil the gasoline there) you can flare the inside of the spacers to match to the two openings.
That mismatch should not be a problem though.
The mismatch the other way round would certainly have to be corrected.
The intake manifold is probably made to accept 48IDA/IDF.
You should check the manifold to head mismatch. More important to match up there because of the rectangular shape.