going to a 99 harness is going to save you a lot of headaches. It's not plug and play but its totally worth it and you'll have some extra fun since its a VET. my ECU recommendation is link, hands down.
yes boosted GTIR. yes to CAS as well. it works well for my setupAre you boosted? I have an Apexi controller and solenoid but dont have them wired up yet, HolleyEFI 3-bar map, genuine GM IAT CLT, etc all wired and calibrated in TS. I've heard (and seen) good things about Link. Might bite the bullet and buy one. Are you running sequential spark and fuel with coils and a CAS, or a distributor setup? I've tried with both on the speeduino and Microsquirt, no dice. All the info I can find is specific to Miatas, not much for Nissan on those setups.