As I mentioned before, I strongly recommend waiting until after the big update for this, because at this point, terrain will be as simple as copying the files and resizing them to half their size. If we do it currently, then for the conversion to V1.43n-F, we have to load all the pieces (incluidng objects, for this one) into an existing-format graphic set, only to then give them all names again (and need an extra translation table) when the new update comes out.
This isn't me saying "you're not allowed to go ahead with this now" - if you want to do it, go ahead - but I am going to say that if you do so now, I will not handle the update to the new version's formats myself because I have warned you that doing it now will mean such a thing will be extra work; you (or someone else) will need to do it.