275/40's will fit on an 8" rim, but according to most tires specs an 8" rim is too narrow for that tire. You'll need to run 5" backspace to make a 9" rim work, if not a little more. 5.5" is probably too much backspace though. It has worked for some and not for others (ah factory tolerances!). A 245/40/17 is going to be way short. If your car is too high with the new torsion bars you need to adjust your torsion bar adjusters, not buy shorter tires. 265/40/17's are not exactly a popular size, there are few choices but not a ton. And that's still only a 25.4" tall tire.
What size torsion bars are you running? If they're less than 1", you shouldn't have any problems lowering the nose of the car with the torsion bar adjustment. You'll need an alignment afterwards, but it won't hurt anything else.
On a set of 17x8's your best bet are probably 245/45/17's or 255/45/17's. A 245/45 is 25.7" tall (decent for the front), a 255/45 is 26" tall. Still fairly short for these cars in the rear, but 50 series are harder to find in that width. 275's will physically fit, and I know Mike Tyler is running them on 8" rims, but as I mentioned the manufacturer specs will ask for a 9" rim for that width, you can make your own call on that one.
