Did you ever get an answer to your question? I have a 2000 Reflection 327 with a 260hp 5.9 ltr Cummins diesel. Recent oil change with filter required 17 quarts of oil.
Just changed my oil and filter. Also 260 engine. My manual shows 19 qts. 14 qts took it to the full mark on dip stick. The other 5 qts must be in the lines and cooler. Just to be sure, I would call Cummings, give them the VIN no. and they can tell you for sure