Just from the little I've read regarding improving old American car suspensions, a shorter spindle is generally a bad thing; at ride height the centerline through the upper A-arms (bushings to upper ball joint) should be near parallel with the ground or pointed slightly upwards for the best camber curve. Apparently taller spindles are a very popular upgrade on GM muscle cars because the stock setup is bass-ackwards in that regard (spindle is too short).

It might be different in your case and I have no experience myself with Mopars that old but I'm willing to bet a lot of the "hardcore Mopar" guys who put shorter F-body spindles on their '50s cars were not too concerned about handling. Personally I'd put a proper aftermarket brake kit on there that's designed for the car, those cars were noted for their superior handling compared to GM and Ford stuff and I wouldn't want to mess that up. If someone makes a spindle for the '50s Mopars that accepts the later disc brake stuff you could throw on a pair of 11.75" Cordoba rotors with the single-piston calipers, probably the cheapest route for good brakes and it's still like 80% Mopar