Another tire question????

[chavez o]

Looking for new wheels an tire combo. Been reading all the posts. So sorry if this may be a repeat question. Currently on my 67 camaro I have more of a pro street look. It is in transition to a pro touring car.Rear multileaf @ stock height wheels are 15X8 out back with 245 60 15, front has 2 inch dropped springs 15x6 with 205 60 15s. No rubbing. I want to go for as wide as possible. I think 275 40 18s or 275 35 19s will fit out back with ??? backspace on an 8 inch rim. And 245 35 18s will fit up front with ??? back space also on 8 inch rim. Anyone have similar suspension set up? Looking for recommendation that work.
and what back space. Any help appreciated