Mr. Ske'. Is the HE in question mounted directly to the engine by means of a soldered on bracket or is it mounted by means of non-metallic stand-offs? If non metallic stand-offs, for sure you will need a grounding strap.
I have no idea what solder was used to affix the tubing bundle to the outside housing BUT if soft solder, you will have to heat-sink that bundle/housing joint when you reattach the end casting. I suggest submersing the HE in water up to that bundle/housing joint to protect it's integrity. You should then have about 1" to 1 1/2" of the HE sticking out of water to solder to.
American Diesel and Bomac are the only two sources of OEM coolers I know of BUT I have seen reference to generic suppliers suggested by other members. As per usual, I can't remember squat...