A search will turn up the part number easily. Just search on "275 part number"
If I remember, the 300HP ISB uses the same 275 injector as the 275 rating. The difference comes from extra pump fueling.
This is not true for the old, marine 12V motors. The 370 Marine injectors are a totally different beast.
The part number is a Bosch part number, not a Cummins one.
Here it is: 0 432 193 635 .
Try the search, it's a great feature. I found this pretty quickly.
Hope this helps-- if you need anything else, don't hesitate to ask.
Hohn