Dont understand why you dont have either the part if you have a starion engine, unless you got one that is from an oil cooled only turbo? But had a turbo that didnt match your engine? Oh about the oil pressure sensor I looked and I did what you said connected it to the stock montero location and blocked off the one in the oil cooler adapter.

89 Monturbo (RIP now but the heart is in the 90!)
90 Montero with 2.6 turbo swap! (close to finished)
88 Starion MPI T3/T4 Magna M8 head.....
96 Volvo 850