It comes down to packaging and mostly where the shocks are going to be located.



Some ideas around this subject are, putting the calipers on the leading (forward side) of the axle as it keeps the brakes (ie the weight of the components) in between the wheelbase for better balance. But on the 68, the weight would be better if they were put on the trailing (rear side) of the axle to offset the weight on the front end. It may be small, but every pound helps.

Also on the 68, the shocks were in a staggered configuration from the factory..... that balances the weight right on the axle centerline.

Really the issues that come into play is the positioning of the calipers to where they are not going to interfear with the leaf spring (or what ever suspension you will run), or interfearing with the shock, frame rail, spring perch or bump stop and keeping in mind where the bleeder is placed on the caliper.

With a 9" I guess your caliper placement is going to be reliant on your shock placement. Start there and trial fit things a few times to see where are happy.