I've seen that before. The only problem I would have with it, is its only going to be able to sync two carbs at a time. That makes the process harder to get all carbs sync'ed properly. In theory, you could still sync your 1 to 2, then 3 to 4 and then sync your 2 to 3. However, I find it handy being able to see the relative pressure of all gauges at once, because they tend to creep a little throughout the sync process.
Then again, the "luxury" of looking at all gauges at once is quite a bit more expensive than the home build device.
I would go for it and let us know how it works. Ever better, if you could sync it with your home built tool first, and then verify your sync'ing with someones real gauge setup.
At the same time, I have to admit, I am using my Morgan Carbtune more than I ever thought I would. Between my bandito and my old honda CB, it gets put to a lot of use. So if you get some spare $$, it might be worth it to get the real thing.
Good luck!
jesse