I'm pretty sure a '99+ Si uses a CKF. I haven't looked at a B16A2 oil pump but I'd put even money on it being basically the same part as the '96+ B18C1's, with the sensor.

Do you remember the tech asking or looking at the ECU? Actually, the blub was ripped from the check engine light and he knew there was a code. Most likely he hooked a computer up to your diagnostic port and read the codes that way. If you put an OBD I ECU, the diagnostic port may not function anymore (I think that was an OBD II addon). Do you know any of the tech's from the inspection place or have a friend who does? Sometimes you can work out a deal where they only go based on the sniffer test or you can just get them put a sticker on. I don't have emissions testing around here so when I get inspected, they just switch the stickers for me.