low and slow - Making the Albin 27 more efficient

I know this is an old thread, but I'm looking for repower options for my Albin 27. The boat originally came with a 79hp Nissan diesel (550lbs) which has since been taken out if the boat and sold off. These boats came with everything from a 61 hp Peugeot Lehman to a 200hp BMW diesel. The most common was the Nissan. These boats need about 100hp to even get up on plane. I think 60hp is too much wasted power on this hull.

I want to repower with a diesel. I'm looking for long range cruising at hull speed. I don't want to get up on plane. The more efficient the better. I'm looking for as economical repower option as possible with high reliability. How small can I go and what might my other options be?

Conventional repower options for the A27 call for the Cummings 4b3.3m 65hp or the Beta 38 if you want to go slow. The Cummings is actually cheaper than the Beta 38--either of these is around $11-13k. The Beta is smaller and lighter.

Given my unconventional requirements--What else can I consider?

Thanks