I think you are correct. the crankcase size is almost the same as the .30 but not quite. I had to look it up inSaito's instruction sheets. It looks like the .40a has about 1mm longer mounting screw placement and the screw mounting holes are 2mm wider than what is on the .30 engine.
The .40a appears to have some performance improvements as it develops a little more power than the earlier .40 does.