I think I would pass on that setup, It sounds a little pricey to me. If you are thinking of running the ladder bars with your stock leaf springs its not a good idea because of binding in the way a rearend moves up and down with leaf springs and shackles. And the ladder bars are going to want to move the rearend up and down in an arch like this ) . And I would guess the ladder bars have metal Heim joints in them also , they will make for a very harsh ride.
I like Chevelle rearends , 64 to 67's are 60 inches wide and 68 to 72's are 61 inches wide overall plus a 5 on 4 3/4 Chevrolet lug pattern. Also check 67 to 69 Camaro or 68 to 72 Nova , they are 60 and 61 inches wide. All can be found in 10 or 12 bolt , 12 bolts harder to find and cost more.
Evilbeef are you in Nor Cal ?