I agree, the teal and orange one might be the same bike. According to the old thread by @deezildennis Dave Grattan's daughter said the Hound Dog has a 5 hp briggs and the Hot Dog had the 3 hp briggs. The brochure for the 400 shows the Tecumseh hs40 was used. The briggs has the gas tank on the left hand side of the engine. That being said the Hot Dog would need the extra room on the rear tire side of the engine plate. I'm thinking that's the reason for the engine plate moved more towards the front tire. Vice versa for the 400 engine plate because the gas tank is on the right side on the Tec. I think your right on those pins being stoppers for the spring rods.