Sweet! Be sure to check over the linkage function after the engine is warmed up. Expansion might not be an issue on a in-line engine, but it's worth verifying all the adjustments are good after it's been run a while.
I'm guessing your carbs have idle jets without cutoff solenoids, correct? Does each manifold have a vacuum port, both the same diameter, you can connect to? I think for the long term you'd be served by investing in your own Uni-Syn, a snail type synchrometer, or a electronic meter that reads manifold vacuum (the Cadillac of the options, IMHO). They make the job pretty easy.
Anyway, there are several things you can do. If you have cutoff solenoids on the idle jets you can run the engine at idle and disconnect each side's jet solenoid's power supply and note the drop in RPMs. The idea is to set the carbs so you get the same RPM drop off, while having good idle RPM when both carbs are connected. Works well assuming the engine will stay running with only half the cylinders firing. A dwell/tach meter can be handy doing it this way, but sometimes the engine's running too lumpy to get a good reading and you end up going more by ear.
Another method is to use a section of tubing inserted into each venturi to listen to the hiss of air being drawn in. The idea is to set the carbs so they hiss the same. Truly the old school method here.
If you've got identical diameter vacuum ports on both manifolds you can make a tool using clear tubing filled with a bit of ATF. The ATF stays in a low bend in the tubing and uses vacuum signal from each manifold to give an indication of balanced or imbalanced suction between the carbs. If the ATF is drawn more to one side you know that carb is pulling more. Search "carb balancing tool" and you'll find plans for many variations of this tool. Sometimes it is necessary to use an orifice in either end of the tubing to slow down the ATF's movement. If you like building your own tools this is an easy one to do and would serve you well.
There's also a cool electronic tool that reads off manifold vacuum. "CarbMate" and "Tecmate" are worth looking at. A friend of mine has one of these with a analog needle and I think it works great.
I really like the tools, homemade or other, that connect to both manifolds to give a more dynamic reading between both carbs at once.
There's a nice mixture of backwoods and more "together" options for you. Some web searching would add to the list, I'm sure.
