I purchased a mechanical Oil pressure gauge for my 91 Sunbird. It is a 2.0 L OHC. What I want to know is how to install this. Do I drill into the oil pan, or is there something already there to screw it into. Any information would be helpful.

Thanks

..whatever you do do not dril lthe oil pan. first of all there's no oil pressure in the pan =P. second its jus ta bad idea. there should already be a threded bung on the block where your original oil pressure sensor goes, im not familiar with the 4 cyl motor but usually its located near the oil filter. gm will often also have extra threded bung right next to it plugged up with caps, if there isnt then what you do is get a T of the proper thread size and corresponding pieces of pipe from you local hardware store and thread it into the block put your guage connector onto one of the t ends and screw in the original oil pressure sensor into the other. im sure someone with better knowledge of that motor could give you more detailed advice.

Why?
Why do you want an oil pressure gauge? I'm assuming this isn't a turbo motor?
Just get the turbo cluster, or the "SE" cluster (same thing without boost) and get the factory GM oil pressure sender and you'll have an electronic gauge in your dashboard.