1st,,I'll partially retract my reference to the EGR pipe I posted early in this thread. This is most likely not your problem as described.
on EGR pipe gasket, I use one for a ford/mazda I matched up.
I'm out of town and don't have the part number tonight, but will post it later.
You really need to do 1st things and cheapest things 1st,,, and listen to folks on here. Parts stores are there to "sell" parts and don't have the time , interest and "sometimes" the knowledge of our older and very special vehicles. Change your thermostat and get an ohm meter and check your engine temp sensor/sendor as per the FSM.

dave h.
'89 Raider V6 5spd;Aisin Hubs;; Gen2 LS: frt. brakes, rear coils;U.C.arms;R.trailing arms;idler arm; rear LSD axle w.disc brakes ;2 battery system for Dog's fan; relocated ECU; custom bumpers;J.Baker receiver;Conferr roofrack; t-bar crank.