Hi Bishka,
Welcome to the forum, and thanks for your requests.
Heightfields can only store one height value for each x/y coordinate. Overhangs have at least three height values per x/y coordinate. This means that to support overhangs, L3DT would have to abandon heightfields and instead represent terrain as freeform mesh objects. This would require a major rewrite of the application, and I have no plans to do this just yet.
L3DT uses a different plugin system than PSP, so plugins for PSP will not automagically work with L3DT (and vice-versa). However, if a plugin developer was so inclined, they could write a plugin for L3DT to load PSP plugins and act as a translation layer for function calls between L3DT and the PSP plugin. It's technically feasible, but it's also likely to be a lot of work. If you can program C++, then L3DT's plugin API is
available here, and if you can't, then I wish you the best of luck in finding someone willing to do the work for you.
Best regards,
Aaron.