pics of 4 link thus far

For a 4 link to work properly the rear end needs to be able to rotate slightly. Are you planning on removing the leaf springs? I assume the bracket with all the holes is for the rear of the axle housing to mount the shocks. Do you have the shock brackets or are you planning on making them? The spacing for you 4 link isn't very good. From the looks of it, they're only about 5 or 6 inches apart. They should be at least 10-12 inches apart and your front frame brackets need multiple holes for adjustment. When you start welding on the rear axle housing, keep it mind if you get to much heat on one side at a time, it can bend the axle housing. Check the link to art morrison below for a good picture of a 4 link setup.
Art Morrison

Pretty much the same theory with ladder bars. The rear end can't be fixed to leaf springs, so if you use leaf springs, you'll need a floater kit for the springs. If coil overs are used, a diagonal link will be required to keep the rear end centered in the chassis, same for 4 link. Rear mounting holes on ladder bars will be in the 7-8 inch range. You will also need a crossmember welded from frame rail to frame rail to mount the forward brackets. The forward brackets usually have 3 holes for adjustment. I've seen solid rod ends used in the rear of ladder bars but spherical are required for the front mounting to prevent binding. Preferable to use spherical all around. If you click on the link for art morrison, you can click on the ladder bar link on the page to see their setup.

Are you going to build your ladder bars too? I can understand wanting to do things yourself, but just buying an already proven system from a manufacturer would seem to be more prudent. Even with ladder bars, you may have to make some notches in the floor pan under the back of the seat and fill them with sheetmetal. Another possibility might be to do an unequal length 4 link set up sorta like a late model Mustang (or old GM) where the upper 2 bars mount close to the center of the housing and angle out to the frame rails. This would eliminate the need for a diagonal brace/panhard bar. The mounts at the frame could be attatched to a tube that runs from rail to rail like the lower one. This is really more for the dare to be different crowd and would take quite a bit of work, but I think it can be done. It's something I'm considering doing to my '65 coupe.

Oh, and the Morrison stuff is good stuff. We used a 32" adjustable ladderbar kit with solid ends all around and the cheap adjustable coil overs (stick regular shock inside an adjustable sleeve) in a '69 Mach I (drag only car). Weld in diagonal lower kit, ran a tube from rear rollbar downtubes and giant holesaw cut some holes in the floor for the coilovers to go thru. Went straight as a string with a race 289/Jerico/5.67 gear combo. 11.08@119. You had to drive it with the SSM bars, with the ladder bars, you just had to hold the wheel straight.