I picked up the plastic Khador jack set as well as 10 magnets to make the arms interchangeable. Last night I sat down to start working on building it, and I learned a few things that I thought others might like to know.
First, if you want your Juggernaut and Destroyer to have different axes, you will need 3 more magnets. There is a single arm piece that can then have the hand and axe attached to it. Since there's only one arm piece for both axes, then you have to use magnets to connect the hands at the wrist.
Second, there are four different heads. I'll probably just pick one, but you could also make the heads interchangeable if you wanted to do so. That means five more magnets.
Three, positioning the magnets is important. You definitely want to do magnet to magnet and not magnet to metal for the joints. The magnets Dave sells are strong, but they don't have an perfect grip on the heaviest arms like the Decimator's ripsaw. For attaching the magnets, I used a pin vice to pre-drill a hole where I wanted to put the magnet and then used a 1/8" drill bit to make the space for the magnet. I drilled the holes deep enough so that the magnet is flush with the surface in which it will rest. The magnets are definitely strong so you will want to be very careful about how you attach the magnets. When you have them all together, they stick pretty firmly together. You will want to take advantage of their combined magnetic fields by doing the same thing when you attach them. If you look at your jack from the front, you essentially are going to attach the magnets in the same layout. I learned this after I put in the left shoulder magnet and was attempting to put in the right shoulder magnet. Without using plastic tweezers, the first magnet was strong enough to flip the second magnet over if I tried to install it with the same magnetic poles pointing towards each other.