To keep the diameter and revs per mile close, I would recommend that you install a 255/40/20 on the front and a 295/35/20 on the rear. This will also give you a cool "old school" look.
I wouldn't try to squeeze a 275/40/20 tire on an 8 1/2 inch rim. The minimum size for this tire is a 9 inch rim. If you install it on an 8 1/2 rim, it will not perform or wear properly.
I've got Nitto Motivo 275/40 on the rear, on my heritage classic rims, and they fit fine with no bulge. So far they have driven fine for past 8 months. rims are a hair narrower than I'd like for this tire, but the nitto tires almost always run a little narrower than other brands of the same size, I'd rather of had 10 inch rims on the rear and had always had 9 inch rims for using 275s in the past, but they work great on the heritage 8.5 inch rims as well.
Use the tire calculator on tire rack. 245 45 20 is the se diameter as 275 40 20. I have no issues running 275 40 on all 4 corners and a 8 in rim. Hardly and buldge