The car can & will handle wider than 8" wide wheels, it really depends on what your trying to do, how low or high you want the car, ride height can dictate tire size some also... But a set of 15 x 8"s or wider on the rear with the proper back-spacing, like 4.5" B-S should fit fine with a 8" rim, if you go wider you want more back spacing, like 5.5" B-S for 9" wide wheels, to 6" B-S for 10" wide wheels {allot depends on the tire size/girth/bulge}, even with a much larger than stock tire, like a 275/60/15 fits with a ton of room still, then 15 x 7"s on the front with a little less or the same back-spacing will fit easily, even with a 245/60/15... that is a great looking bigger than stock, common type wheel/tire combo... you can go even bigger easily... they have a ton of wheel well, in these 1968 B-Bodies, you can put allot of tire/wheel in/on them a 295/50/15 or a 315-345/50/15 even {or 16"-17"-18" wheel diameters}, on the rear, with the right wheels & Back-spacing or ride heights... you need the proper back-spacing with the proper width/diameter of wheel/tire you choose, the wheel well gets narrower as it goes up toward the top, the leaf springs in the rear will become an issue if you go too much B-S vs rim width & tire girth, the outer lip will need to be trimmed if you go more than a 10" wide rim {12"-13" wide tire girth/bulge}usually or not enough B-S in the rear wheel/rim... the front will rub on the inside of the wheel/tire too, on the sway bar, frame or inner wheel well, with too much B-S also at steering wheel lock in either direction, anything wider than about a 9" wide & 5" B-S up front is a really tight/tricky fit {it can be done thou}... there's is a great/accurate tire fitment tool sold by Summit Racing or Jegs, for like $70.00 it's a Percy Tire Fitment Tool, well worth the money spent, you can adjust them to many different wheel diameters & widths, different bolt patterns, different tire diameter & widths/sizes, especially if you plan on getting the most tire, you can without any rubbing issues ever...