[JimsCAL]

Are you sure it's an Atomic 4?. Very unlikely in an 89 Catalina. Note that when Universal switched from the gas A4 they called their marine diesels "Atomic". I believe a few of the later Cat25s had Universal 5411 diesels installed.

 

[JimsCAL]

As I posted previously, Catalina offered an inboard diesel option for the 25 in later years. Here's the brochure. Note the option for a Universal Model 12 diesel inboard. I doubt you could even get the larger 4 cylinder A4 in that boat.

http://www.catalinayachts.com/wp-content/uploads/2016/12/Cat-25-Brochure-Spec-Sheets.pdf