Ok, dug one out for you. Spacers are roughly 2.15mm wide, and center of one cog to the center of the next cog is roughly 4.15mm, which will be the more useful measurement for what you are hoping to achieve.
Correct, the 9-speed cassette has an extra spacer behind the largest cog, so even though it fits on an 8/9/10 freehub body just fine, in terms of shifting the cassette is effectively more narrow. The 10 speed has an extra cog riveted to the largest cog, sticking out a bit past the freehub body. The 11 speed has 2 cogs riveted on to the 9th cog, sticking out even further past the freehub body, and requires a hub that was designed with 11-speed Linkglide in mind, otherwise you will likely run into issues with the derailleur cage hitting the spokes.
Using the your old shifter and derailleur will not work, or at least won't work without something like a J-Tek shiftmate. To get a properly indexed drivetrain without using the Linkglide shifters and derailleurs, you will need to find the correct mismatch of shifter and derailleur. For example, I got a functioning drivetrain with a 9-speed 11-36 Cues cassette, 11 speed chain, 10-speed Shimano Dyna-Sys MTB shifter, 9 speed Sram 1:1 derailleur. However, because the 9 cogs are packed in a slightly smaller space, the low limit screw needs to go in further than normal, and it hits against the parallelogram when attempting to shift into the smallest cog. Grinding away the spot on the parallelogram where the screw was contacting fixed this. The same drivetrain with a 10-speed 11-39 Linkglide cassette and a RoadLink added should also work without having to grind anything.
These two pages should be useful for trying to come up with a working combo for your bike:
https://sheldonbrown.com/cribsheet-spacing.html https://bike.bikegremlin.com/1278/bi...compatibility/
According to the second one, the Dyna-Sys shifter is intended to work normally with a derailleur that has a ratio of 1.2, while the Sram 1:1 derailleur has a ratio of 1.1. Finding a shifter with a slightly higher ratio than the derailleur seems to be the trick.
Haven't put enough wear on them yet to know how true this claim is, but I wouldn't be surprised if there is at least a little truth to it. Shimano's marketing also claims it shifts under load much better, which is absolutely true. I've got one setup with a Bafang mid-drive kit, and it even shifts fine with 500w of power put into it. On the other hand, Shimano's marketing claims it will reduce the amount of parts a bike shop has to stock, which is complete BS, as there are already millions of bikes out there with Hypergilde drivetrains, and they will continue to exist and need service for decades, even if new bikes were to completely switch to Linkglide.