If you want optimal power and don't mind a loud exhaust swap it over to 70mm single outlet. Dual exhaust was a stainless steel, mid muffler/ dual rear mufflers. Regardless of brand it was only 60mm.
Before the previous trackday @ Sydney Motorsport park last weekend we decided to quickly service the S2000 (oil/oil filter/gearbox oil) and quickly changed over to 70mm single outlet titanium...
Aftermarket cams in a B18c7 stock doesn't seem like a bang for buck mod. Change out those JDM headers to Toda or alike headers, high-flow cat mated with your RM10A.
Shorter ratio's helps engine with no power to get going. With h22a/K24 you actually need longer gears to ultilize the torque. H2B was design to fix the hideous driveshaft angles in Honda swapped cars...
Abit of fiddling around with hoses and pipes (a/c place will make new hoese/hardlines). Most tricky bit is mounting the a/c condensor since the original mounts can't be used.
At least do rod bolts (APR). You'll need a B20/VTEC conversion kit, b20b8 block the rest will be fitting all the parts together. If you aint gonna change rod bolt you'll be limited to rpm (7200rpm)
Using K20 flywheel will open up more options to clutch kit replacements. If your stuck and on a budget AUDM K20 flywheel will suffice (lighter then EURO). As for clutch, heavy duty or sports organic...
Im not 100% certain there could be a feature in the Hondata Flashpro that can rectify speed inaccuracy. Even so, flashpro is the way to go for AP2 S2K.
Gain are to be made with bigger t/b you'll need to remove the intake manifold and bore it out same size as throttle size. So will cost vs gain beneficial, IMO no. Upgrade the FD if you havnt already...
If "forced induction" is against your religion then power can be made n/a. Question is - building a high powered n/a with great parts will tend to last, once you start cutting parts out yes it'll...