1972 C30 dually drop spindle install HELP!!

[Junkpyl]

Hi all, I've looked around but cannot seem to find a definitive answer.
I just started installing my drop spindles from Bell Tech this morning and all is going well until I noticed the brake caliper mount is very different. The spindles are listed as 75-91 and they dropped right onto my ball joints with no issue. haven't gotten to mounting the rotor yet and hope there are no surprises there as well.

These new spindles seem to need a separate mount cradle for the caliper that is not in my possession.

I bought them used but in like new condition.

Anyone know what I'm up against?