DT-Rings

I've got three eyepieces with FL 5, 8 and 13. I used to view with my 2" Focuser and that was great.
Now I'm trying to view with 1.25" focuser/barrel but I've mixed them up. Is there a way to identify which barrel belongs to which eyepiece?. The three 1.25" barrels have the same height but I could notice different lens diameter.

https://www.baader-planetarium.com/en/downloads/dl/file/id/92/product/1208/hyperion_eyepieces_technical_data.pdf

The telecompressor slides into the baffle of my Celestron 8SE SCT but is not secure and slides out. I use a 2" Baader Click-Lock and a 2" nose piece that attaches to my OAG. There is nothing securing the telecompressor inside the baffle. How can I make sure it does not slide out?

I am thinking of buying an Alan Gee MkII, I am mostly confused as its visual use and which diagonals to use with it. I have a 9.25 SCT (non-HD). Is is only recommended to use with 2" diagonals or can I use it with the smaller T2 diagonals such as the T2 BBHS Zeiss prism? I was thinking of using that with the #16 T2 2" nose piece holding the Alan Gee and the T2 1.25 with diopter adjustment #8. I would be using the Baader Hyperion aspheric with 1.25 nose piece as well as other Hyperion eyepieces with 1.25 nose pieces. Would the combination of the aforementioned be best? I only have been thinking about using the prism because I want to get the widest and brightest view possible visually, and I also want to use the diagonal for the future purchase of binoviewers. I also don't want to by another 2" diagonal especially the click lock as I already have a Celestron twist-lock 2" diagonal.

Looking at the Protective T-Ring with filter chamber, it does not look like there is much room to grip and thread in a 2" threaded filter. Is there some tool available to insert and remove the filters like the pin type face wrench? If not how does someone insert and remove a 2" filter without touching the lens in such a small space?

Also, now that there are five different Canon EOS R camera models released, do you have any plans to make a version of this Protective T-ring with filter chamber that can directly connect to the Canon R Bayonet?

In another question you answered that the optical length of the Protective T-ring with filter chamber is actually 11,8mm and not the 12mm listed in the product specifications. Which value is correct?

Also, when using the Protective T-ring on a classic Canon EOS DSLR (44mm optical length) or with a new mirror-less Cannon R with their EF-EOS R adapter (20mm + 24mm optical length), this would put the total optical length at 55,8mm or 56mm.

Considering a Baader 2mm filter, we would then want to add 0,6mm to the total optical length to compensate for the extra focal length caused by refraction through the filter. This would then mean the proper optical length should be 55,6mm with a filter installed.

Based on the stated 11,8mm or 12mm optical length, that means the optical length would include an extra 0,2mm or 0,4mm in optical length respectively.

Will this difference in optical length have an impact? I ask because in another question I asked about the UFC system you suggested fine tuning spacers to get to exactly 55,6mm optical length when using the UFC system with a 2mm filter.