The three Sendai class ships were built with a hangar below the pilot house. Prior to the war, the three ships were refitted as destroyer flotilla leaders, but not all received the same exact mods. Sendai and Naka had their pilot houses modified by cutting back the front corners to give a faceted front similar to the newer cruisers. Additionally, Sendai had her pilot house lowered when the former hangar was reduced to a normal, single deck height. (That was probably why her fore funnel was shorter than those of her sisters.) There is no record of Jintsu receiving a similar bridge mod, and that difference between Jintsu and Naka is reflected in the bridges of the respective Aoshima kits. Jintsu and Naka also had the torpedo tubes upgraded - the forward tubes were removed and the hull embrasures plated over. The after tubes were made quads and reloads provided. Sendai's tubes were not modified. Naka was built with the "swans neck" bow and and Jintsu had her bow so modified several years prior to the war. So there were a number of detail differences between ships. (And if you look closely, you can see those bridge differences in the drawings Dan posted.)
As for differences in the kits, check the following links:
Jintsu:
https://www.1999.co.jp/eng/10250974Naka:
https://www.1999.co.jp/eng/10250975 (Check the #5 5.5" gun mount.)