D4600 power unit saga

Hello, I am a new member trying to help out my buddy. His family bought a used D4600 power unit back in 1952 (Serial 4H8083SP). They converted a water powered sawmill to diesel with this engine and it has run the mill since. Several months ago the aluminum top on No 5 piston somehow came loose and broke apart. The broken shards were exhausted out the stack. He was able to shut down the unit almost immediately to avoid any further damage. He was a toolmaker by profession and is an excellent mechanic. He removed the head over 4,5 and 6 and was able to saw through the bent conn rod to extract the piston. He was able to locate a donor engine from the same era, but upon disassembly he found the pistons and valves were of a totally different design and were not usable. I have been trying to help by scouring all over trying to find usable parts. I joined this group because you folks seem to have a better pulse on things that do anyone else. To start, I'd be interested in finding a piston and conn rod. He has the original parts book for this engine and it shows a very distinct cup top to the piston. I am going to try to attach as many of the photos I have to help make sense of this. Any ideas would be appreciated. Thanks, Dan

PS I tried to upload a bunch of relevant photos, but it keeps telling me that they failed to upload. I am not the brightest bulb on the Christmas tree so can someone tell me how to load pix?

Include any part numbers that are on the parts from both engines, that will help determine what will interchange.