The problem with installing a different engine (it can be done) is that it may not be economically viable either and depending on where you live, could be against the law due to emissions, etc.
I'm not familiar with the Freelander at all but a quick read seems to say that the cylinders are designed to project above the engine block a certain amount to help seal the head gasket. Eventually the liner sinks for whatever reason and the head gasket lets go.
Some other vehicles in the past such as 70s era Subarus, Renaults, etc. have used this design. In the case of Subaru the liners sat on copper gaskets of varying thicknesses designed to project the cylinder liners up a certain amount. Copper being a soft metal of course and combined with 15k mile intervals on head retorques would cause the liners to sink and the head gasket would go belly up. Bad design very prone to problems and it sounds like the Freelander is afflicted with roughly the same disease.
It may be time to get rid of the vehicle as is and consider it an expensive education unless a new engine is guaranteed (in writing) to have a redesign and the shop will stand behind it (also in writing) for X miles.