You start to be quit experienced now 
You have probably checked many sources when you looked possible game ports? Could you share that information to us? What ports could be possible, what would need to do, what experince would be needed? Do you have some kind of list? Like Alien Breed 3D - TKG code is ASM and completely mess, almost impossible. etc? That would be helpfull, for those who are looking for possibilities.
Yep I've done this a few times now so this is what I've learned when choosing some older (open source) PC software to port to AGA 68k.
1) Needs to support 8bit obviously
2) Resolution should be 320x240 max (320x200 is better)
3) Obviously needs to use a software rendering engine (no 3D hardware required)
4) Must provide C code and not rely on X86 assembler
5) Must support big endian
It's best to choose an open source project where someone has already gone to the trouble of cleaning the nasty old X86 code up and making it system independent (most of those old DOS games are a bit scary).
Most of the time the thing you want to port will use the SDL so this is currently the steps I typically perform for porting a project
using gcc 3.4 (AmiDevCpp).
1) Try and get it working using the old 68k RTG SDL, replace any missing UNIX functions with Amiga equivalents (eg DOS functions).
2) Once it's basically working using the SDL, I replace each SDL area (sound, input, timing, graphics) with Amiga/AGA equivalents (obviously test each stage as it's removed).
3) Remove all debugging/test code that might slow it down (writing to the console or log files is very slow) .
4) Remove any features that would be too slow under AGA (eg multi-player network support, fancy graphical effects, CDROM support).
5) If possible remove multi-threading and run-time type checking (C++).
6) If possible replace any core rendering functions with assembler (my Quake ports only use a tiny bit of assembler but they use it in the right places).
7) Replace memory copy functions and memory allocation functions with their Amiga equivalents.
I'm currently trying to develop a very basic AGA SDL, if I can get this working it would really help with porting more stuff to 68k AGA.
