Both my '86 2.9 and my '87 2.9 had/have the EGR position sensor you have pictured. In fact, I've never seen any other type on an '86 or '87 2.9. The vacuum line from the sensor is connected to the exhaust side of the EGR valve. The sensor detects the difference in pressure when the egr valve is opened by the EGR solenoid.
If you get the vacuum lines on the vacuum reservoir reversed you will have no vacuum to open the EGR valve. Contrary to the Innova Code Reader manual, the Haynes manual states that code 33 is "EGR valve opening not detected". The vacuum reservoir has a check valve in it to prevent vacuum from escaping when the engine is not pulling a strong enough vacuum to reliably open the EGR valve. The vacuum reservoir port facing the front of the truck goes to the vacuum tree, the rear port goes to the lower port on the EGR solenoid, the upper port of the EGR solenoid goes to the diaphragm side of the EGR valve, and the port on the exhaust side of the EGR valve goes to the EGR position sensor. I would have mentioned the vacuum reservoir earlier, but I made the mistake of relying only on the Innova code reader manual to explain the codes.