70 dart tire & rim options???

Need some help. Can anyone give specifics on maximum wheel and tire sizes for a 70 Dart. Completely stock suspension front and rear. 8.75 rear axle. Looking to fit widest aftermarket wheels and tires with stock body panels, rear leaf spring locations, etc.

Can anyone give specifics on 14" vs 15". Rim width? Rear and front offset for maximum width and clearance?

I was thinking of 15" rim with possibly a 245 or 255 / 50 series (low profile). This is a big block (383) conversion car. Will have discs in front. Drums at rear. All LBP (4.5") bolt pattern.

Appreciate any help I can get and thanks...

Daren A.