Well, I just went out and looked at my own 88 (it's a five-speed, but that shouldn't matter...)
The Sync sensor is the three-wire job in the distributor.
The Oil Pressure sensor is near the base of the distributor, and has one wire.
The only other sensor I can find on the right side of the engine is the LPCO sensor (Low-Pressure Cut-Off) on the A/C reservoir - which obviously isn't part of the block.
I'm out of ideas - got a pic? There are a couple variations on the oil pressure sensor - and I think one of them may look a little like the piezo sensor on the other side.
Once again - I'm willing to trade information for information...
(Oh - I didn't see anything like that on my 87 or my 89, either...)
5-90