wheel and tire fitment on a 66 chevelle 300?

[Lenie]

Will 20x10 wheels with 6" backspacing & 315/35/20 tires along w/ 17x7 wheels w/ 215/45/215 and 4 1/2 Bs fit on a 66 chevelle 300? If not, is there a way to adapt them? If the rears won't, could I use a spacer and put on a narrower tire? I Want to be able to lower the car down over the whees. Everything on the car is stock. Was wanting to go 18's and 20's but found this deal. What would be a good fit with the 18's and 20's comfortably?
Thanks Lenie