Looks like they bolt on. There may be enough room to cut the flanged entry out of the bottom of the plenum. Make it 5/16" longer on the farther end, and reverse it, then weld. This will move the actual opening and the flange for the runner by the pitch distance difference (8mm).
The linkage should be examined: what is it now, and what do you want it to be?
No personal experience, but I would not try to run the engine on the center (#3) carburetor alone - that #3-4 port will drink all of it.
The most likely choice for race is all 5 in synch (all levers attach at the same length from the throttle shaft).
The street choice with progressive (staged) linkage is probably #2 & 4 for primary to attempt (!!) some mixture distribution. The progressive part will look very similar to any other progressive, even V8, as to how to calculate lever lengths. I have some more text on this here:
http://victorylibrary.com/mopar/log-2.htm
