I recently bought a Land Raider Redeemer and noodled around a bit trying to figure out how to make the sponson weapons swappable. I though about using magnets then discarded the idea because I didn't think the magnets would be strong enough and the fuel tanks for the flamers are too big to fit if the center post is glued in. I decided to replace the entire center post. All you'll really need is some 3/16" styrene tubing and some 3mm round rod. I got both of them at the local model train store.
First, cut a length of tubing to fit the interior of the Land Raider sponson. This is what you're going to hang the weapons from. Next, file or cut a slot into both sides of the 3mm rod. You need this so that the targeter will fit onto the end. It may be hard to see in the picture, given that it's white on white.
The first thing we're going to make is the pin that holds the weapon in place. Fit the targeter to the end of your rod and glue. Drop this through the two holes on the sponson, mark where it exits the lower part, and trim to fit. You may want to leave a little bit exposed to make it easier to extract later.
Using a round file, file out a shallow groove on both sides of the sponson weapons, right at the mounting hole. This will give the model glue a little more surface area to work with. Here's what my flamer and hurricane bolter assemblies look like.
You're pretty much done. All you have to do now to swap out weapons is to pull out the center pin and pull the weapon out. Here's the flamer in place, without the side guard.
To change to the hurricane bolters, just position over the holes and drop the pin in.
To be honest, I haven't quite figured out what to do with the side shields. I'm thinking I might just glue them to the flamers and fabricate another set of shields for the bolters. If and when I acquire a set of lascannons, I can add this set in the same way and they'll have their own side shields.