67 Valiant tire and wheel fitment

I can't answer for the front, but for the rear, unless you use offset shackles, you won't get a 275 in there. As far as using the B body rear end and the wheels you're looking at, I have only one question...
How do you feel about radiusing the rear quarters?
I have a 76 Duster 8.25 rear in my 69 Valiant and am running 255/60R15s on 8" wide wheels with 4.5" BS. It's close to the spring and the wheel well lips.

I am for sure planning on moving springs into the frame rail, already have the stuff. I think you answered my question for me.

Your rear end is about 56" WMS to WMS. Either axle I am contemplating using will be about 59".

It sounds like springs moved in, narrow the Explorer 8.8 to 56" and run 15x8 wheels with 5.5" BS should get there. The car is kinda rough, and I am a bit handy with a welder etc. so if I need to weld and move things that is ok.

Thank you, I will commence with the narrowing process on the 8.8.