They're both P75. All P75 is really, is just part of the part number for all OBD1 and OBD2 non-VTEC B18 ECU's. I'm pretty sure there are some internal differences between the auto and manual ECUs, what they are I don't know.

This whole "I'm getting a swap with an auto tranny because it's cheap" idea sounds a bit sketchy to me...how cheap is it? LS swaps aren't very expensive to begin with.