Not sure magnaflux will work. I've heard of blowing minute iron particles (like grinder tailings) through ports in aluminum parts so you can see into it better, but I'm not sure how visible it would be through the deeper passages.
The problem with the LIM is that the coolant comes in and out through several points and travels in different directions. You have to have a really good understanding of coolant flow through the engine.
Xray would work.
But you'd have to shoot ALOT of views. I think I have enough to maybe model it in 3D.