Hello
First to check would be the float level from the carbs and have the float wightet or just 4 new ones. Go trough the carbs first and have them preadjustet as good as possible. Don´t care to much on synchronization. Just turn it to run "smoth" when warm.
Then have the ignitionside checked and drive the car a bit. While you wait for cooling down to check the valves you can look at the face from the sparkplug and have messured compression or have a leak down.
Would be nice if you could checkwhat type of engine you have.
If the engine# and the type# are missing or your engine looks puzzled togehter then you can have a mixed engine with different heads or different pistons ( Everything is possible ).
After you set the valves maybe cheked the overlap timing, have a perfect ignition then you start synchronizing the carbs.
If you do that before its just waste of time
As you have low vac on cyl 6 I have to make sure you talk about the cyl 6 from the engine wich is on the passengerside far forward.
Grüsse