It will be 5x4.5". Ratio's can be anything, same with the Sure Grip, might have one, might not. Depends on the how the '67 was set up.
Should fit pretty well, I have a '68 B body rear in my '74 Duster. The '67 B-body rear is a little bit narrower than the '68, it should actually make your offset about the same front and rear for your rims.
As far as the perches, they need to be moved. A-body perches are at 43", '67 B-body are at 44". Yes, you can pry the springs out by a 1/2" per side, but keep in mind what that's actually doing. You're side loading the springs and bushings pretty significantly. And you're pulling the springs out wider, so, you're reducing the amount of space you have for tires. Yes, you can do it that way and make it work. But its absolutely the wrong way to do it.
When I installed mine I actually moved the perches in to 42", and used a 1/2" offset spring hanger/shackle kit. I now have 295's on my Duster with a little additional trimming on the quarter flange.