So far, I've managed to get the following third-party packages installed:

• JEDI (JCL and JVCL), using their installer, which works great.
• Virtual Treeview (again, using the installer).
• ADOM (problematic; following the instructions didn't work, and I had to remove the Utilities package and let the main ADOM package build it during its own build).
• Graphics32 (very problematic; eventually had to comment out a reference to GR32_BDS2006 package before I could get it to compile).
• UniSynEdit (worked fine).

I've been cautiously testing Delphi 2005 to make sure it hasn't been damaged by any of these changes, and so far it's building IMT just fine. I've also been able to create and compile an application which tests Graphics32 and UniSynEdit successfully, so it looks like we're on track for an IMT port.