I agree Jimmbo, but to this day "restrictor plates" are still discussed, and I think they're an internet myth. I hate to see people wasting their time trying to get more info on them.
Honda 35, 40, 45, 50, and 60 hp engines all share the same short block (block, crank, rods, and pistons). The heads, which also carries the cam, I suspect are just slightly different, with the differences not visible to the naked eye - only by a coded dab of white paint. They use the same intake manifolds (other than the injected 60). The 35. 40, 45, and 50hp carbs, which also appear identical, may also have some very slight differences, though they share the same gasket kits! ECM's I have no idea. On these engines, as well as the 75/90 4 cylinder engines that are set up nearly identical like the 3 cylinder engines, there is NO restrictor plate!