No original barrel. That is a Jupiter barrel, Russian made.
Also, the original wartime or pre-wartime Sonnar has two small 'ears' of that are knurled and the rest of the aperture ring is smooth.
Looks like you have a later (possibly Jupiter) lens block and a certainly Jupiter barrel. The Carl Zeiss name ring might be the only thing that came from Jena.
Three characteristics of a genuine Sonnar:
- It would have two screws of different size set close to each other in the knurled focus ring
- It would be marked 'm' for meter instead of 'M'
- It would have coatings that are mostly honey and have a sheen of purple.
Lenses that lack any of the above are at least tampered with (CZJ Sonnar and Jupiter are close to identical in design and can easily be swapped out) and possibly completely Russian with a CZJ name ring. Which is what yours appears to be.
The lens barrel certainly is no Summarit (won't even fit) and the amount of digits on the serial number is correct. Wartime Sonnar lenses would have serials ranging from 270xxxx (CZJ production) up to 285xxxx (Russian supervision of CZJ factories).
Lenses marked '3K' (for Zorki Krasnogorsk) and '1947' or '1948' should be met with utmost suspicion, the 1948 lenses could be genuine but the 1947 lenses are very likely to be re-engraved Jupiters.
As to whether it's a good lens: it sure can be if it isn't already. The Sonnar design isn't very complicated but many lenses were slapped together in the later days of the USSR since the amount produced was more important that the quality of the product.
Early lenses are often manufactured with great care and are more often good lenses, if they aren't used up that is.
You should at least shoot it for a while and see if you like it. I bet it will surprise you, sometimes in a positive way, sometimes not so much. I have a simple Jupiter-8 from the 1990s (gloss black paint barrel, basically still the same lens) and I love it.