What would be the compression ratio on a 1982 Ford 200 inline 6?

What amount would be normal, 136,000 miles

Added (1). What octane should I use? 87, 89, 91?

8.7:1
A compression test should yield 175 lbs.
To be "acceptable" it should be with in 80% of 175 lbs. (wet cranked) and no more then 17 lbs. Different between cylinders.

I'd pray for 140lbs at that age. If they are all running about the same, it will be OK, but lack power and MPG.

9.2-1 is the ratio. Or where we looking at what compression readings in a cylinder ought to be? That will vary according to how it was driven.serviced and individual material composition etc.
with that mileage it can vary according to if used for many long highway normal ( not high speed) cruising or all town driving .stopstart /towing?
water rates are very subjective but anything above 150.lbs/square inch per cylinder is ok. Balance of errors ( different readings ) to be within 10% ideally. If we have say one colder down by more than 10% versus others then we may have an issue on that cylinder. Remove plugs when cranking and check each cylinder a outlined for pressure test. If? Low? ( sub 140?) or one cylinder or more is out of condition. Eg vey low. Do try a wet test. ( cranking test again after engine injected to a cylinder and cranked a few times. That has effect of sealing piston rings and should raise compression test readings on all cylinders. If not? Then we have valve seating issues on that cylinder.
as to what octane. Use the manufacturers rated as outlined in owner manual. No point using higher one.