[nanard289]

Hi Jon
In complement of Gary's explanations, IDA and IDF carbs have a different fixing pattern. IDF body center line is 90mm and the larger IDA is 120mm. It means that they should be installed in a dedicated manifold and there are not switchable. For engines with large displacement using IDA, it is better to add a third progression hole to improve ... engine progressivity. Start with a small drill of 1.2mm and then test it. If it not enough you can enlarge it to 1.5 or 1.8mm.
Sorry for the missing pictures but larger attachements are not possible