OK, I have a 1987 Cheer Men PT42. It's probably a very, very similar hull to yours. Ours was re-engined in 2003 with John Deeres, but they are still 225hp, (6068 turbo units).
On our last long trip, which lasted 6 weeks and covered approx 900 nm, we averaged about 1.9 nm to the gallon...