Well that is very much possible with the old terrain. With the advanced terrain you can specify a split value which determines how it is broken up and scale, so you may be able to match it up better. What I would so is export a .x and a heightmap and play with them until they match as closely as possible. This is how I done 3dws terrain .x and heightmap (which sadly cannot be an exact match though pretty close).
[edit] I just tried and you can get them pretty close, but since the advanced terrain uses extra smoothing and 1 more poly wide it isn't perfect.