Ah! I get it now.
Ball joints complicate the matter, but the whole job may not cost as much as you’ve been quoted. I will probably need new ball joints too at some point, and the press-in thing means I’ll be getting the job done by someone with a press and some knowledge, rather than DIY. I would be interested to hear your guy’s quote on that job. I’m thinking it should be about $100 to take the old ones out and press new ones in. They sell for about $15-$20 each, I believe.
I think I paid $300 for my adjustable beam. Might have been $200. It came with the seals, bearings inside, adjusters welded in, etc.. I just had to rattle can the new one (the paint they do isn’t so great), disassemble the old one, slide the leaves in the new one, grease it up and re attach the trailing arms. It was not that bad a job. My complication was a bit of rust on the frame head, which I didn’t really fix. If you don’t have that, you could consider doing the beam swap yourself.