The Monroe Super 500s were the premium HD shock back then. Worked on all vehicles, too. Had a 1 3/16" of 1 3/8" piston diameter, which is one determiner of "HD" or not back then. All Chrysler front shocks had a 1" diameter piston, due to the size of the tube the shock went into in the front stub frame, but had stiffer valving to compensate.
We got some of the Chrysler "parts book" hd shocks for our '66 Newport. At the base of the shock housing was stamped "M.A.E.CO.", which the old line Chrylser service manager said was "Monroe Auto Equipment Company", which replaced the earlier "Monroe" stamping on Chrysler shocks.
The pictured shocks were their aftermarket line, not OEM replacement, as I recall.
Just some thoughts,
CBODY67