The chassis went together nicely. My plan of adding the Crusader I MG turret worked out nicely. I just thinned out the plastic a bit to help the turret stick. It probably did not need it because I've found the magnets powerful enough to attract through at least one layer of plastic.
It was after I cut out the turret parts that I realized that magnetizing the options was going to be a bit more difficult than I had thought. There's two turret tops but only one turret bottom. So, to swap between the Crusader III and the earlier models, I would have to magnetize the top and bottom. And of course, the two turret tops have completely different hatches, with earlier versions having a slide top. And the Crusader I/II has two different types of gun, a 2lber and a 3" howitzer.
18 magnets later, I have a completely swappable tank able to be Crusader I complete with auxiliary turret, a Crusader II, a Crusader II CS, and a Crusader III.
At least I have a pattern to use for the remaining three tanks. I'm going to pay greater attention to polarity in this one so that all the parts will be swappable across all of the Crusaders. This is an extra pain but it will be a benefit when it comes time for gaming. I reckon that fiddling with polarity has added about 30% extra time, but I'm getting a bit smarter in dealing with it.