Those are Hitachis rather than SUs. They only use one of two springs, so it's much easier than an SU. The lighter spring is used on A-series. L-series engines used the heavier spring.

You do not need a tool to meausure vacuum, you can stick a piece of hose into each carburetor and listen to the sound. Adjust the balance screw until the sound is even.

If that is a stock A14, the stock A12GX carbs should run well on it.

To identify the needle, remove it by taking out the set-screw. The number is stamped on the thick end. M83 was the original GX needle