‘71 340 Duster Front Drum to Disk with Factory 14” Rallye Wheels - Problems

I would grind the caliper to fit, it won't reduce the strength of the caliper by much if any.
The suggestion to use spacers would work too, even though it's not ideal.
I would tend to grind the caliper to fit, because the wheel is hub centric, and spacing them out is not the best idea...