Any drawback to keeping the drum spindles on my 66 Valiant?

I will definitely be upgrading my front 10" drum brakes to disk in the future. It seems to me like the options for disk brake conversion seem to fall either into changing out the spindles to later model disk brake spindles or keeping the drum brake spindles with a conversion bracket to the caliper (Leed or Wilwood). BTW, I do plan to go with 4.5" bolt circle and 15" rims when I do the conversion. The thing I wonder about is the small upper ball joint used on the 66 and the larger upper ball joint used on later models.
I saw one manufacturer of tubular upper control arms that suggested that their big ball joint UCA can be adapted to the early drum brake spindle by reaming out the spindle (MagnumForce). Is this a legit, viable solution? Is there really any drawback to keeping the small upper ball joint? I'm not really stuck on the idea of tubular UCAs but just the question of any limitations of staying with the drum brake spindles and the small ball joint.

Thanks - Jim