Those are the most-desirable carbs for the Six Pack, in my opinion... you've struck gold. If I'm correct, those are the long-discontinued R4791/R4792 Holley Super Stock race carbs, evidenced by the 3 accelerator pumps and the driver's-side fuel inlets on side-hung float bowls. The side-hung bowls were necessary for clearance, as the center-hung bowl will not clear on the rear carb with a metering block. Check the list number on the choke tower on the center and let me know if I'm right--I'm going from memory on the list numbers.
The linkage is pretty cobbled-lookin', but those screw-type stops are actually a part of the original Edelbrock linkage used, as would the rod on which they're installed likely be. That bent linkage bar was apparently the work of someone who didn't have all the parts, and didn't understand how a lever works, but it's somewhat close. With a good shot of the valve-cover-level view of the driver's side of the carbs, I could pretty-easily explain (or Photoshop) what the linkage should look like.
They're way more tuneable than the stock carbs since all three use metering blocks with jets rather than the metering plates used on the stock outboards. Of course, you now have three pump shots to tune as well, but that's no big deal. You're going to have to learn how to drive 'em, though. You can't just mash it from a dead stop unless you've got a hell of a lot of engine underneath 'em and a lot of stall in the converter. Think of it not as a Six Pack, but as a 1355CFM triple-pumper (the R4791 is rated 5CFM higher than the OEM center carb).
The last time I bid on a set of those on eBay, my $575 max bid wasn't even in the ballpark. I think they went in the neighborhood of $800, looking no better than yours and without any linkage or fuel lines. Keep in mind, I had absolutely no use for 'em at the time and had better places to put $600, but that's how highly I think of that setup. I don't know or really even care what you paid for the setup, with those carbs you've seriously scored.
Congratulations, my friend!