Its a mash of 720,d21,521 and more. Only 2 people know how to do it. Jim from top jimmy motorsports in tracy ca and a dude in mexico.
Jim completed my ball joint conversion earlier this year. Its amazing to have a proper setup. Total cost with parts fab and labor is about $2500 or so. I dont have an exact price due to he also added straightening the front end after my crash.
I can provide the info if needed.
Make that 3 people as I have had a ball joint front end on my 521 since 2005, I even have power steering, but I didn't flip the 720 upper control arm as my work truck is not lowered.
All they are are 620/720 lower control arms or one can use the hardbody LCA with the pressed in balljoints, 620 LCA disc brake bushings, I have 620 tension rods but it appears you used 521 tension rods, lengthened(3/4") 720 upper control arms, and the disc brakes you want in between the ball joints, I have 1990 V6 hardbody dual piston calipers, but the 1985 720 disc brakes are popular, I had everything used or I bought it cheap as I could as I didn't have that much money to throw at it, I also still use the torsion bars.
I didn't have to make any changes to the shock towers as I am using stock shocks also, I likely have less than $300.00 into mine including the Hardbody disc brake assemblies I bought from Yello620 for as I recall $175.00 used, I was using 620/early 720 disc brakes at first as that is what I had.
But I had to figure out everything to make it drive correctly myself as I did this on my own without forums(2005) as I didn't even have a computer back then, Mike K came over and looked at how I did it, I don't recall how he found out, maybe he came to look at how I did the power steering, that was a long time ago.
The key to making this work is the upper control arm connection, the stock 521 UCA mount bolts are not big enough, if I had it to do all over again I would drill the mount holes out to except a 720 mount bolts, I had it aligned and the guy at the shop said I had everything within 2 degrees, it drove great, it corners like a race car when empty, but most of that has to do with the rear suspension, as I can haul loads on my truck.
I am actually retiring this frame this winter, it was never meant to have power steering and it has taken it toll on the driver side front frame.