this link
https://www.tapatalk.com/groups/czechpistols82792/452-ultra-lux-wood-t17523.html
Among other things, implies a different factory originally made just the 452 ultra lux. Also, it was originally made for a company as a custom order which didn't accept the rifles so they were put on the US market at a discount. They sold well, encouraging CZ to make additional runs of them and gradually letting supply and demand set a new price for them. Also, for whatever reason, there was a small run of around 190 units made with a walnut stock.
post 4 has some interesting information:
begin snip
The Ultra Lux was not made by CZ-UB. I think it was made by CZ-Strakonice - an entirely different company.
I have read other posts here that state that CZ-USA does not acknowledge this rifle as one of theirs (and was therefore not sold by them), and I have read some posts that state that the poster received information about the Ultra Lux from CZ-USA! I suspect that the first situation is the correct one (and the second scenario was probably confusion with the CZ-UB Lux model?).
So . . . . . as the Ultra Lux is not a continuation of the CZ-UB line up, there is no reason that it should be expected to "fit in" with the CZ-UB product range.
The stock is as it is and is not a model up or down from any CZ-UB products (no matter the similarity in names) but is just different, and ditto for the action and barrel - they are peculiar to the Strakonice factory (no matter how closely the action resembles a CZ-UB product).
end snip
Please note, however, that the same poster later in thread comes to realize some of his information on the history of CZ is in error, so take the above with a grain of salt.