There is a definite lack of information concerning these basses, so thought I’d contribute to the pool of information. From what I can gather, these were made in Sverdlovsk, USSR - offered as an alternative to the original bass model (Ural 510L) to remedy the neck/body balance problem by utilizing the body of the Ural 650 guitar.
The Ural basses are pretty frequently put down for their purportedly terrible sound, but i am not seeing that here at all. frequencies are round and full, bass is responsive