This is a repro of the [ill-fated] oil cooler on the F2/3 bikes. It did not cool the oil measurably, as the airflow into the face of the non-vented cases isn't much. Most of them today have been removed because they typically weep oil between the cooler and the engine cases unless both of the large O-rings are the [properly] oversized (as in, extra-thick) O-rings that Honda offers directly in the 750K4 engine parts listings, and the oil bolt is tightened so tightly that it wears the threads. There were various aftermarket "fix kits" for this at one point: one of the more successful ones used a stud thru the oil cooler to mount it to the engine first, then you could change the oil filter normally by using the shorter (earlier) oil bolts, like the K0-K8 and F0/1 bikes used. The stud was Loctited into [cleaned] threads in the oil galley of the case and stayed there with the 'cooler' while you changed filters normally.
More often, this cooler plate was drilled and tapped for hoses, and the center hole blocked by making a special stud with oil ports from the filter and into the engine thru that stud, to use as an adapter plate for a real oil cooler (like the old Lockharts, Hookers, or Action Fours mini-radiator) that mounts up onto the horn mount. These often sat a slight bit crooked, though, because the horn mounts were not necessarily welded to the frame at 90 degree angles...
