Looking to order 17s

I'm looking more and more into ordering 17s for my 68 valiant that has bbp disc brakes up front, bbp 7.25 rear (eventually 8.75). I'm running a hellwig 1.125 sway bar and 2800 as springs. In a 17x7 about what back spacing would I need to fit a 205/40R17 and a 245/45R17? Sorry if rhis question has been done to death.