I found that tile problem while ripping the maps, but I couldn't see any correct tiles in the graphics. I've attached all the tiles the game uses. (The full map is on the HOL entry
If you can see tiles that would work, it shouldn't be too hard to insert them into the game. It's not quite as simple as it seems, as the game is composed of about 12 submaps, each with it's own set of tiles for that submap. As you walk into a new area, it copies the relevant tiles into the buffer and decodes the map (as it's run-length-encoded).
I guess tile 371 appears to be blank so might be able to be drawn into, and possibly one of the high tile numbers like 511.
Incidentally, I never checked how the game stores the collision/walking state/height of each tile, hopefully that's a separate map and the submaps are literally just indexes to the graphics. If not, it might be a lot more work to fix those 2 tiles!