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if the wheel is 8 inches wide they will work but they will be sitting in the wheel wells pretty far. They will need 1/2" spacers to put them out in the correct location.
I am looking at new wheels for my 85. Will a 43mm offset work fine and clear everything?
At 43mm, that's only a 5mm difference in offset or just under 1/4". You shouldn't notice that. What you should be careful with is clearance between the inside of the wheel center and the calipers.
Wheel width has an impact on tire fitment. If you are keeping the stock 255/50-16 tires, you really need a 9 to 9.5" wide wheel. 8J most likely refers to the width and that will be too small for the 255 tire.
Also verify the bolt pattern. GM wheels typically are listed as a 5 x 4 3/4 pattern but the specs are actually in mm or 5 x 120.6mm. GM OEM lugs have a 60 degree taper; if the new wheels use a different taper, you will need new lug nuts.