If you have the proper deeper multi-leaf spring mounts on the rear axle the '67 lower brackets should be able to be used I think. They had stuck 3 leaf Nova springs on my car WITHOUT changing the spring perches on the rear end, just used longer bolts and left one of the pads out, NOT GOOD. Made it easy to go back to monos though. On '68's not only was a lower mount moved due to staggering the shocks, upper moved as well so I don't know how you'd stagger them without messing with at least one upper mount.
I know this is of no help and not the cheapest alternative, but if I was building a 1st gen pro-tourer I'd have to go with one of the 4 link kits available and ditch the leafs altogether. Some of them even "Bolt-in."
EDIT: Check out post #15 here:
Mono vs. multi leaf spring perches: