Personally I was surprised to see someone assembling a crossover this way. There is no reason for the individual components to be laid out in the pattern that matches the way the circuit would typically be drawn. Not everyone would draw the circuit exactly the same anyway. There is reason to orient inductors to minimize interference among their fields. The inductors should be located first, then the other components however they happen to fit. It would never occur to me to do it the way he does it. I use a piece of hard board and start by tracing out the locations for the individual components. I drill holes for the wire leads and also for the nylon ties to hold down the component. I don't bother with a heat gun but instead I use either some silicone goopy glue or else just some double-stick foam tape. I insert the wire leads through the holes while placing the component, then fasten the component to the board using a wire tie. Obviously I do the soldering on the other side, using any scraps of medium gauge wire that are handy. I look it over to make sure there isn't a place where in incorrect contact could accidentally occur. Anyone who can't sort out where to run the stranded wire (jumpers) after flipping the board over should maybe stick to preassembled crossovers.
As I think about it, if I were selling a kit speaker of this sort, I would probably include two paper templates that would add about two cents to my costs. One template for laying out the components on one side of a piece of hard board and another template showing where to run the jumpers on the other side.
If the intent is for people who've never done anything like this to assemble the crossovers, he should point them to some of the better YouTube videos that explain what kind of solder is best, why flux is needed, what a cold solder joint is and how to avoid it.