Scot Trucks (see current series of features), when it converted its C1 tilt cab to a conventional, had a pretty wide cab too, but apparently conceded to Hayes. Several other manufacturers who converted tilts cabs for conventional use, notably International, could boast of good width too.
The favourite Kenworth and Peterbilt conventionals had quite narrow cabs by comparison, and large truckers found it quite confining to get in and work in small cabs.
I have found another contender for widest cab - granted it might not be exactly an over the road truck.
The sad fate of Euclid - a name once synonymous with off road dump trucks - is that the name was dropped in 2004 by Hitachi, the eventual owners of the company.
Nutshell Euclid History
Euclid Electric Hoist Co, founded by the Armington family in 1907 lead the field for heavy off-road machinery. They spun off the Euclid Road Machinery Division as an independent company in 1933 and built
their first dump truck in 1934.
GM purchased the Euclid Corp in 1953 but were forced to sell its US operations in 1968 after years of anti-trust litigation (which they lost).
White Motor Co bought the US interests, but GM continued to build and sell the same trucks and other equipment in Canada and the UK, and later in the US under the Terex banner. GM had the advantage of GM engines and Alison transmissions and GM differentials - the real guts of the Euclid.
When White went under, its truck division was sold to Volvo, but the Euclid brand went to Daimler Benz. DB sold it in 1984 to Clark Michigan which formed a 50/50 joint venture with Volvo in 1985.
After other twists and turns Volvo Michigan Euclid formed a joint venture with Hitachi in 1993, but by 2000 Hitachi was sole owner of VME, and they phased out the Euclid brand in 2004.