B16a and if you can find 1 a B16B from the old old type R (97-00) with 185bhp
the 300 bhp is possible but it would cost so much youd proberly be cheaper buying a new car, and the engine would need rebuild a hell of a lot. ive heard of th B16a getting 270 from heavy engine work and a supercharger.
even the s2000 kicks out 240 stanadard only really goes to 350 in most tuning cases
if your a newbie stick to basic things you could do yourself such as panel filter or induction kit, be wary as induction kits have a side effect of losing low end power in smaller engines
sports exhaust ( off the shelf kit ) can be fitted in a afternoon with relitive ease, the civic ones easy enough. the cat can be a prob with the heat on the bolts but that was the only trouble i had changing mine
i dont think that theres any difference having 2 back boxes it just means theres a split in the mid section to allow gases to both boxes so its dearer as 2 boxes are in use. mine cost £50 off ebay for a second hand one. powerflow done my one for ma prelude for £312
if your wanting figs for each honda engine
Wikpedia Honda B engine
hope it helps