I'm really suprised at the EPA and actual mileage figures. I had a 94 GSR with IHE mods that always got 31 mpg. Never better, never worse with about 50/50 mixed driving. With the taller gearing on the LS I would think mid 30's all the time would be the norm. I'm sure you could get 38-42 with a standard civic d15/d16 with the lx transmission and better with a cx/vx transmission. The lean burn motor would be more of a pain to swap IMO. The shape of the integra looks much more slippery than the hatchback civics which should equate to better highway mpg. Not sure your Integra is that much better looking than the vx though.
Here's one I restored.