as well know, the bigger the engine the more heat created. Honda dealt with this in 1975 with the 1000cc water cooled gold wing (which by todays standards is tiny). Which became the 110, the 1200, the 1500 (six cylinder) and the 1800.
V-twins got larger and larger relying on air cooling. By the twin cam 88 and 96 oil coolers were a Harley add on (been after market for years) but as they got larger and into the 107 the full touring models added liquid cooling to the heads, and the striped down touring (e.g. road king) had factory oil cooling standard with a fan upgrade. The touring models also have an optional fan that sucks air past the back of the engine cooling and giving relief to the driver and rider.
Our S&S at 124 ci is as large as the water cooled Goldwing 1800. The transverse mounts is a perfect setting for air flow at speed. But this is why Morgan added the fan for speeds under 10 mph, as there is nowhere for that heat to go at idle
