correct me if i'm wrong, but...

i have a '91 civic hatchback, and i'm pretty sure it has one of the d-series engines in it. i'm tryin' to crank some more horses out of it, but i'm not sure if it's worth puttin' money into. it has about 113,000 miles on it. i also want to stand a chance against the rsx, civic si's, and integras. check out my sig for the mods. would it be worth it to do a swap? i want to take the cheapest route, but get somethin' that's potent enough to stand a chance, and highly upgradeable in the long run. what do you guys think. b-series? if so, which one? or should i stick with my D?