Your machine is basically a Yanmar in JD green paint. With that said, don't look at just Deere parts, look at the vast Yanmar parts.
The key for the exhaust manifold is to know where the muffler is plumed in.
Attached is the Yanmar 3TN75 parts manual. Look over the exhaust system. Then look around for the Yanmar parts. These parts are global, found on Yanmar tractors, excavators, Komatsu earth moving machines, Yanmar gensets, name brand gensets, Yanmar Marine diesel engines, John Deeres, Cub Cadets, and many other places like ThermoKing refer semi trailers, etc.
You don't need to swap out engines. Just get a matching exhaust manifold.
The Yanmar 3TN75 to the JD 3TN75RJ version is typically a 90% or better mach up.
Manual compliments of the, Yanmar Tractor Owners Group on GroupsIO with 35+ years of community involvement. We are the largest vintage to modern Yanmar community on the web.