Heh, cool, great to see you again.

Getting the original levels working in Survivor should be easy in every other respect but the heightmap. I think we made Survivor heightmaps more accurate, so that could cause some problems. I tested exporting the third mission of SG to SGS (Survival mode) and it seemed to work fine, so I'm not sure what the problem with heightmaps is (but I'm sure there is at least some problems, maybe they're not visible on the surface).
Anyway, the bigger problem was that all the buildings were gone. Shadowgrounds Survivor uses blocks for buildings, and the original used large building models. In theory it should be easy to just copy all the required buildings to a mod Data\Models\Buildings directory, and then it could work. Also all scripts would have to be copied. Other than that, I don't see why it wouldn't work... Of course, with all the building models, the mod size would be quite big (I'm thinking 500 MB or something).
I can give it a shot and try to make one original SG mission playable in SGS, and then report how easy/hard it was... Not sure when I'll have the time though (should also test the Sentry thing from another thread etc)...