[ReelMagic]

Being more pro on diesels than gas for a 37 or bigger the Yanmar 315 hp diesels as a replacement would be a direct replacement WRT to shafts, props (may need a pitch/diameter change) but are similar to the 454 gas you have... Several manufactures offered Yanmar 315's as well as gas 454's due to the similarities that allowed them to use the same shaft, struts, props (minor change required). Fuel economy is better with the Yanmar's but don't believe the expense justifies them. From experience, my buddy has  Yanmar 315's in his 37 Cruisers Inc. express and has found out the same boat w/gas 454's is faster but uses more fuel (est. 10%) so the diesels don't justify the expense... Additionally, they were made for cars/trucks used offroad and not for marine use. Marinizing them for marine use has dissimilar metals touching each other that caused electrolysis. Additionally, the oil pans are sheet metal and rusted away due to the exposure to a salt environment. M2C