I'm no expert but I'll give it a shot. Ruttman uses seat post style handlebar clamps, Harrison uses
motorcycle style. The steer tube on the Ruttman is larger in diameter. Ruttman had a clutch to jackshaft that drove a right hand drive sprocket while using a jackshaft brake. Harrison used a torque converter and mostly a left hand drive sprocket with internal brake. I have seen some with the torque converter driving a jackshaft but unsure if they were original. This also brings to attention that Ruttman, having used a regular clutch, the clutch cover was different too. Ruttman had a flat clutch cover while Harrison had the bump in it to accommodate the torque converter. The axle strap angles are different, Ruttman's appear to be 45 degrees while the Harrison appears to be 60 degrees in relation to the lower frame tube. I'm not sure if the handlebars are the same, I know by the time the Pac-Mule came out they were different. As far as being made by the same manufacture, I can't say for sure but it sure looks like it.