Complete clueless idiot: please help me install linuxcnc v2.6.11

hello, I am trying to download linuxcnc 2.6.11 which is the version used by the sherline lathe that I will get in a couple of weeks. They charge 900 dollars for a computer with the linuxcnc which is absurd so I wanted to try doing it on my own. I got a dell optiplex 7010 and downloaded the latest version of ubuntu.

I then tried to download linuxcnc 2.6.11 via the terminal with many errors every time (with the help of chatGPT) with the following commands:

sudo add-apt-repository 'deb linuxcnc.org/ buster base 2.7-rtai'

sudo apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv-key 3CB9FD148F374FEF

sudo apt-get update

sudo apt-get install linuxcnc

I tried using precise base and other bases along with the associated keys

each time I get errors such as "unable to locate linuxcnc" or "skipping acquired file XXX...does not have the component 2.7-rtai" or ""the following signatures couldnt be verified because the public key is not available: NO_PUBKEY XXXXX"

edit: another error is "the repository 'linuxcnc.org buster inrelease' is not signed. updating from such a repository cant be done securely and is disabled by default

Can someone please please help me with some idiot-proof instructions on how to download this older version?

I haven't been around enough to know 2.6 but 2.7 is available at linuxcnc.org/iso as an iso. Might try that?

It shouldn't be that hard to get it running on 2.9.2 instead of 2.6.
Do you have the ini and hal files?

I do not have the .ini or hal files onhand as the lathe has not arrived yet, however, I believe sherline has it posted on their website here: sherline.com/wp-content/uploads/2016/04/...027070277.1718319041

I do think that I will end up just trying to get it to run on a later version of linuxcnc, perhaps I will try downloading 2.7 first to check it out

I'd try an install of Wheezy, it'll have 2.7 but should be able to be made to work.

I'd be wary of AI and the like, you know with "d1v3r5ty is strength" mumbo jumbo. If it finds enough information saying the sky is Cheddar Cheese that's what it'll tell ya.

On a side note, has anyone seen "AI sign language", think about it, how often does AI get hands right ?