The 90 has a ball-and-pin tow-hitch. It has a (very worn) LR ID plate on so I assume it's original equipment.
The pin is missing.
The hole is 25mm (or perhaps an actual inch?)
The only pin I've found in a quick on-line browse is 25mm diameter and 200mm long - seems a tad too long to me? And will 25mm fit or will I find it just too snug?