I read something about these trucks maybe 20 yrs. ago in Hemmings I believe. If my memory serves me correctly they had 1 engine & trans for each drive axle. The 2 trans gear shifts were hooked together so both were shifted at the same time when loaded. When empty the gear shifts were separated so one trans could be put in neutral and that engine shut off. Of coarse throttle and clutch worked in tandem loaded or empty. Hope my memory is working right.
That is hands down one of the most interesting trucks I've ever seen. I like the pics in the second link. They just pull the tray out with the two flatheads like it's a kitchen cabinet drawer. I know it wasn't a speed demon, but how did they control it if one engine lost some power or rpm's as compared to the other?