Hi You may want to hunt up an old belt drive compressor from a refrigeration system.
The first part is to set your engine up to run properly hot and get as much heat as possible from the exhaust with a non- compressor method, direct to the water.
Running a compressor has inherant inefficiencies- mechanical losses.
You will want to generate electricity first. As a load to help the engine run properly.
A diesel is not like a gas engine in that the engine needs a load to make heat. Ask any truck driver, their engines don't warm up with out a load.
The engine it self will radiate a lot of heat from the castings. For the ultimate in heat recovery you will have the engine in an insulated room and aircondition the romm to keep temperetures under control.
I don't want to be a party pooper, but you need to decide what you really want to do.
Dennis