Old USA Trucks
 

Came across this

http://www.delphos-ohio.com/Holdgrev...es_campers.htm

"The most interesting Relay was a 6 x 4 "Duo-Drive" which used two Lycoming straight eight engines located side-by-side with a total output of 275 hp, each driving a rear axle via separate air-operated five forward and two reverse transmissions"

Relay was a sad, short-lived truck manufacturer. It was formed in 1927 when a consortium of bankers acquired the assets of three struggling builders: Commerce, of Ypsilanti, Michigan; Garford, of Lima, Ohio; and Service, of Wabash, Indiana. All were consolidated in Wabash under the Relay Motors Corporation name. Relay built eight different models, with capacities of one ton to four tons, all with Buda six-cylinder gasoline engines and four-speed transmissions. We're not certain which year Relay is shown in this photo, but most Relay trucks had stamped louvers in the sides of their hoods, rather than hinged cooling doors. The tractor's wheels, which look like discs but have a demountable rim, were unique to Relay. Relay would go on to build a monstrous truck called the Duo-Drive, with two 420-cu.in. Lycoming straight-eights mounted side by side, before the firm was liquidated in 1932.

Unable to find a photo of these Duo-drive trucks

Bedford built a twin-engined artic tractor in the late 1960s.
The engines were side by side in a 'spread' chassis frame and connected together by a morse chain drive.
First (and only) time out it accelerated steadily up Cutenhoe Road Luton from the factory, but by the time it reached the Chaul End Test Track at Caddington it had twisted the frame (insufficient cross-bracing) and you could slide a housebrick (on end) under the right front wheel . . .