Ah, another ecomodder stuck with a ricey engine. I have to deal with a torquey 98 Civic EX coupe that makes 127HP... Your motor makes 108 I think, so you have a bit of an easier path but we have the same final drive ratio (4.25) with my 5th gear at .702 and yours at .771. What a bummer that you don't have the original D15B6, or especially that HF transmission.
Looking at my fuel log you would see that the lower 50s MPG is attainable with a more powerful and heavier car than yours, but I never really go 70 unless I'm rolling down a hill. Based on my experience and what I've read, I think your goal is possible, but it's a lofty goal and you will have to make some drastic changes to any or all of the following: your driving style, your engine/trans, aerodynamics, LRR tires. Ditch the CAI and get that engine breathing some hot/warm air right off the exhaust manifold - that should help a bit too.
Personally I'd list it as an Si. That would make you look better as an Si with that lightweight HF body versus making your results look worse among genuine HFs, but more power to you if you can beat them out with your car.
Good luck and welcome to EM!
