I am rebuilding the front end on a 63 Valiant and installing 10" drums from a 66 Dart.
If I use K7021 and K7023 (65-72 disc lower ball joints) instead of K785 and K787, do I need to drill-out the mounting holes to a larger diameter, or are they exactly interchangeable?

The 7021/7023 do have the larger bolt holes then the drum lbj's. When doing the KH disc conversion on my 71, I didn't think I had to get the lbj's (originally had 9" drums) but when coming to assemble I found out otherwise.

Infact I believe thats the only difference, bolt hole sizes. But are you sure 7021/7023 are appropriate for 10" drum conversion? Rockauto and kragen both list seperate ball joints between disc and drum, but don't differentiate betweeen 9" and 10" drums.

I just searched again and found a post that explains it.
The last entry by Doctor Dodge wraps it up, but Doug Ahern confirms that the disc lower ball joints can be used as a HD replacement on drum brakes. My 10" drum assemblies have 1/2" holes, like the 9" drums.

http://slantsix.org/forum/viewtopic.php ... =groupings