Never heard of a 660 Hi-Clear. 660s are not Farmalls. They are either industrial, riceland (maybe), or wheatland tractors sold under the IH label. 660s have planetary hubs. Never seen a dropbox for that setup in any parts book. Two dropboxes are necessary to lift Hi-Clears
The 660 diesel has 282 cubes amd is run at 2400 rpm. It develops 80 hp.
The IH 660 is loosely similar to a 560 Farmall. The Farmall could have been built as a high clear. The 560 motors only run at 1800 rpm. The radiators are three inches shorter. Most all 560 Farmalls had a fast hitch. Fenders, if equipped, are clamshell style vs full coverage on 660s.