i have ls1 fr/rr setup on my 69. 18x7 w/225/40 fronts. 20x8.5 w/255/35 on rear w/no problems. i had 235/40 on 18x8 up front b/4 the swap but changed because i thought there would be issues, but i believe they would work.
I have some spacers that I will let go fairly cheap that will work for corvette wheels, not sure about camaro wheels. Fronts are 1.25 and rears are 1.75. You can measure and see if they would be in the ballpark.