I have an IR Model 2340-E 5HP, 60 gal air compressor.
Measurements of the holes seem to be the same as what you show. The slots are 9.5" end to end and 4.5" on center. The holes are 5" on center front to back and 6" on center side to side (the dimension you show as 5.5" from the front of the holes).
Here is the info from the side of my motor: