73 kframe on 72 abody

is the new K frame un-bent & in good shape?
you need to see if any local A body guys have a parts car or test k to verify-- these should bolt up to all 67-76 cars with minimal effort.
if K is good then you have to get your bent frame rails fixed to match the factory specs--
I would not use a die grinder I think you are creating another issue,
the shoulder on the k bolts are chamfered to tighten the K to the rails you don't want to mess with that mounting area.
Lawrence