I don't know which Briggs or Honda model is made where, David. Joe Carroll or someone else will be able to tell you the answer, or what physical properties of the engine to examine to find out.
With regard to engine size and power, I doubt you would be able to make any use of anything more than say 3 hp for a 17" mower: the machine will just accelerate to the speed that corresponds to 3,500 engine rpm (the maximum speed the engine's governor will allow) whatever engine you use, unless you are on a fantastic slope. Reel mowers will not cut long grass, so you won't be able to overload it that way. Essentially the original engine was sized to suit the task that mower can undertake. However if you did find a way to exert more load, the clutches would suffer a higher wear rate, especially the drive clutch which is used a lot more than the cutter clutch. There would also be a possibility that the cutter clutch would slip while fully engaged, due to overload - especially if its spring has been in use for quite a while.
