[Seacraft84]

I would look into a 250 or 300 suzuki (4stroke). If you had the floor raised and the transom strengthened up I would go for the 300. My father had a 300 on his 2000 25' Seacraft and it got awesome gas mileage. Not a speed demon, but efficient. Cruising about 3.0mpg. I bet it would push a 23' in the upper 40s loaded down and get almost 3.5mpg cruising.
I had a 2001 225 2 stroke Yamaha on a 1984 23' I redid and got upper 40s light, even hit 50 when I first put it back together, and mid 40s loaded. Cruising speed was about 2.2mpg That was with a Stainless Marine bracket.
I raised the floor 3" higher than the factory floor and my "plan" was to put a 300 suzuki on it. Boat self bailed awesome with the higher floor.
That being said a used 300 suzuki would be great.
Me personally I would stay away from the 300hpdi. The 150hpdi and 200hpdi were good motors though. I had a 200hpdi and loved it. Buying a used one make sure all updates have been done.
I will probably go with a 200hpdi on my 20'MA I own now.