Just loosen off the adjuster bolt for the torsion bar on the lower control arm. Just take all the tension off of it until it's loose then go to town.

You could also either count the number of turns, or sort of measure how far it is sticking down so you can get it close for the ride height when you put things all back together again.

anyone have the correct 9/16 bolts i need to bolt the disc lower balljoints to the spindles or know where to get the right ones?

need ideas on how to drill out the ball joint holes to 9/16ths. I dont have access to a drill press and my drill is not big enough to hold a 9/16 drill bit..?

a 9/16 bit should still have a 1/2 shank on it. You may call a local machine shop and see what they would charge to drill it for you. That, or if your local high school has a general shop or metal shop program, you may check there as well. Not a lot of schools have shop programs anymore. offer to buy pizza for the class, you would be suprised.

Don't back off the torsion bars unless you know you're going to get the car realigned. Changing the ride height changes the alignment. Jack one side up, pull the wheel, put a floor jack under the LBJ then separate the Upper BJ from the spindle. Put a jack stand under a frame rail then lower the jack to take the weight off the LBJ.
The LBJ bolts can be had at a good hardware supply store. Get 'em with a shoulder for the depth that goes into the spindle. Bring the drum brake bolts with you.
If the LBJs are shot now is the time to change them. Same for the uppers. And the disc brake LBJs ain't cheap, but are cheaper than drum brake LBJs. RockAuto will have them.
You DO know ya gotta change the master cylinder and put in a disc brake prop valve, yes? Can't run with a drum brake master cyl. Get a master for a 73 manual disc A body. If ya need a disc brake prop valve PM me.

Moper440, thank you for posting this as I'm about to do the same swap and some of my questions would have been exactly like yours. I think I got all the answers I needed.