Link to the video please?
The problem is, that I don’t think there is anyone drawing blueprints for fusion engines, at least not until the thing has been demonstrated as an economical power plant.
The only guy that is working on fusion space engines that I know about, is this guy: http://luke.eng.uci.edu/ahcheung/
There is a paper there about it.
And single-stage? The best option if you want to have single-stage, is to have two engines: one for landing and taking off with high thrust, another for outer-space flight with high specific impulse.
