In addition to what TC mentioned.

With shorter spindles, the camber will change quicker during suspension movements.

In an extended suspension situation (like on the inner front wheel during sharp cornering fi), the upper ball joint angle could exceed its designed angle of operation and perhaps fail sooner (in time).

If you don't mind going to 15" wheels, you can fab your own discbrake conversion, keep the stock spindles and keep it all Mopar in the process too.
I put '73 Chrysler discs on my '60 and '62 Chrysler NYers while maintaining their stock spindles.