You are partially right...
The story is a bit more complicated...
Zetor started teh development of the UR2 Crystal range, but the communist central office insisted on involvement of
Ursus of Poland, to spread the development costs.
A small group of Polish engineers worked in Czechia from 1964 to 1968, helping with the 8011 and 8045. However, their influence was small, because Ursus hadn't been developing engines or tractors since WW2. They have built Lanz licenses and Zetor 4011 licenses.
Zetor built the engines and first transmission compartment, and Ursus manufactured some parts of the transmission. UTB/Universal tractors of Romania, built the driven front axle.
The Zetor 8011 was Ursus C-385 from the Polish factory.
In factboth tractors were identical, the difference was that the cab doors of a Zetor were hinged at the front end of the door, and the Ursus doors at the cab. Furthermore, the sheetmetal parts that Zetor painted red, were painted yellow by Ursus.
The Long 900 and 910 are built in the Ursus factory, and the sheetmetal parts that Zetor painted red, and Ursus painted yellow, were painted blue on the Long.
These are reliable machines, great pullers and ALL parts are available through the Zetor PDC parts distribution network.