I have the Heritage setup in an Billings African Queen. I would not worry about going too fast. Keep in mind that although the engine will run fast on the workbench, it turns much slower in the water because of the power required to turn the prop. I think you will find that any attempt to throttle this engine will result in stalling it. The problem with having a single cylinder, single-action steam engine is that it is not self-starting. If you were to throtte down too low and let it stop, that's it! At that point the only thing to do is restart the engine by hand. This is difficult to do when the boat is out there in the middle of the pond. That is why I installed a small electric pump inside the hull. If the engine quits, I turn on the pump by radio. The pump is powered by an old speed control from an airplane. The pump sucks water in under the hull, and squirts it out aft, under the waterline. If you don't have a second way to power the boat, make sure you always launch the boat from the downwind shore, so the breeze will carry it back to you. Another thing that happens with the Heritage is that wind may blow out the fire under the boiler.

The ultimate in steaming is any 2 cylinder, double-action engine. Wilesco makes a fine v-twin, and PM Research makes a v-twin called the "#8". (I have both, and also enjoy the Gage TVR-1A.) Both allow you to start and stop the engine, and have variable throtte all with only one servo! You can have complete control of your steam boat with only 2 channels. Of course both of these v-twins need a larger hull than the small fantail.