I admit I hadn’t thought about vertical alignment!
I will check that out when I have completed the last part (rigid joiner) of the mid assy and assembled it.
Have just bought a dial indicator which can show dimension differences down to 0.01mm. That should reveal the truth about alignment!
If necessary, I plan to ream out the appropriate bolt holes in the rigid supports and shim until the twin tubes are vertical in both planes.
I should find out in the next couple of days.