RE: 1/2A Size Boat Club
Here's some of what hardware I have collected for my projects.
Sterling Models (out of buisness) used to offer 1/2A powered boats also, and had their own line of hardware to help complete them. Brass flywheels and universal couplers pop up once in awhile too on eBay.
Throttles can be put on Cox engines. Some even come with their own throttle sleeve or throttled exhaust castings. The carb I have pictured is a vintage aftermarket Tarno carb.
Cox did make what they called an .05 RC which was an .051 displacement TeeDee engine and only produced in a small number. It had a similar standard carb such as the Tarno I show plus a very nicely done bullet style muffler, but they are pricey and considered collector items. You just have to comb eBay for most of whats mentioned, unfortunately.
As far as an inexpensive way to set up for Cox power is to find a production reed valve type with the plastic backplate. Those usually go for less than $20 and you can fit any size fuel tank you want up to them, and get an RJL replacement head from MECOA to keep glow head costs down.
Something you might wonder about in the pictures is the turned aluminum cylinders with the small black set screws, which are actually flex couplers to go on after the flywheel to adapt .098" flex cable to replace the brass universal and solid drive shaft items that come with the stock Dumas hardware package.
The couplers were custom made for me by Offshore Electrics. The reason they had to be custom made is Cox engines have a pecular thread size comming off the crankshaft, being a 5-40 type thread. Nothing exists with those threads that would work.