del sols are prewired for VTEC... so swapping your engine, ECU, and harness should be about as direct as possible
if you want to make your S into an Si you will also need the rear disk brakes with the lines and e-brake cables... be sure to grab the proportioning valve while you are at it
you should also grab the cluster as the tachometer is different
theres probably other things i am forgetting but those are the main ones