Changing Fork Travel and Tribal Knowledge

It's pretty awesome that Rockshox forks (some) can have the travel adjusted. This will be saving me gobs of money as I go from a frame that requires 100mm to 120mm of fork travel. All you need supposedly is a longer air shaft, and it's only about $25! The stanchions are already long enough, how cool! The tribal knowledge aspect of this adventure is I can't find any documentation that describes how to convert and what parts you need so I called rockshox. The rockshox guy was super helpful; he took my serial number and gave me the part number to go to 120mm travel on a solo air SID XX fork 2015 (also for reba too): 11.4018.021.000

RockShox documentation lists the air shaft sizes for wheel/travel sizes. Part numbers would have been nice here

But almost no retailer lists the part number. The first airshaft I bought was listed incorrectly and was for a 26" fork, ugh. Universal cycles does list the part number: https://www.universalcycles.com/shopping/product_details.php?id=67483&category=701

Now I'm waiting for this airshaft to arrive and I'll report back on the conversion.

Here's the photo of the 26" airshaft. There is no marking on the shaft but it's it's 7 1/4" long, then it's a 26", not 29". Notice the part # ends in 005, not 000, but who could be bothered putting that anywhere in the website description!

Here's the correct (I hope) air shaft

Yup, I measured and it's just a hair over 8 5/8" so matches up with 222mm in chart.