The main challenge in getting AGI onto the C64 is graphics. From what I understand, both the bitmap modes and the character/tile modes are insufficient to accurately display a full EGA picture, due to limitations such as the number of allowable colours. Additionally, the C64 is really designed more for tile-based graphics (40x25 I think).
To be honest, I'm not that familiar with the C64 either. I'm very familiar with the VIC 20 but that's definitely not an option. The graphics on the VIC 20 are far too limited. On the C64 though, I don't know this as absolute fact, because AI told me this, but apparently three of the colours can be different every 8x8 character? - I asked AI what it thought about the graphics limitations on the C64 in relation to AGI. It suggested that AGI pictures in general don't use a lot of colours per 8x8 block, so maybe in most cases it might look okay. - But there would certainly be some cases where it would need to use a different colour in certain pixels due to the limitations. I compare that with the Apple II AGI graphics, that also look a bit less than perfect, with various colour artifacts clearly visible. The C64 might be able to use raster effects, or maybe some stationary sprites to fill in bits that don't otherwise look good. Some of the games that have come out on these old retro computers these days are quite amazing, so there are bound to be tricks used by those devs that could be applied.
I reckon the most promising approach is to not have the engine actually run all the drawing commands in-game, but rather to have a conversion tool which pre-renders and picture into tiles, and then builds disk image(s) containing the converted resources.
Might require a lot of disk space, if disks are your target. I think the C64, even with the modern SD card options, would still be restricted by available floppy disk space for the disk images, so you'd be switching "disks" a lot. One of the annoying things about the Apple II AGI games is having to swap the disks all the time. I don't have a physical Apple II machine, only an emulator, but it is rather annoying. - I think a C64 version of AGI might need an alternative way to load data, like a cartridge with lots of storage space that it can very quickly load from, rather than from disk. Maybe with a REU, something can load all the data into RAM up front, so that it becomes really quick changing rooms.
I don't know anything about how the Apple II interpreter worked (i know this was used for KQ at least). It might be easier to try to port that to the C64 instead. Either one would be a fun challenge.
The only AGI game that didn't come out on the Apple II computers was Manhunter: San Francisco; all the rest did. I guess by the time that game came out in 1989, they didn't think it was worth releasing an Apple II version, although they did release Gold Rush, which is interesting. Someone could probably take the interpreter from the Gold Rush game and the data files from the IBM PC version of Manhunter: San Francisco and create an Apple II version of the game.
Regarding porting the 6502 disassembly to the C64, it is funny that you say that. I did set out trying to do that after creating the Apple II disassembly, but ended up getting completely stuck in some kind of loop with the AI that spanned over several days. Burnt through a lot of AI credits and it kept going around and around in circles on one particular thing. And with the code all being written by AI, I didn't feel like I could take over. I'd be quite happy to pass it over if you like, in case any of it is useful. It might even be a good approach, for someone else to take over, get their AI to analyse what is there at the moment, identify the gaps, look for existing bugs, etc.
