I've got the 0.98 Eprom source code with the RS Debugger source code. The MAME hard drive image with the file can be found at:
To download the file, it is at http://www.USwingNut.../Files/MAME.zip . The code has been up on WHTECH for years as well. Look for the Bootdisk1.hd image under an EPROM folder if you want the zip (~170 MB). That was a zip file I created as some folks were having difficulty getting things up and running the first time.
Now, the swan image code/source is a bunch of data statements where I disassembled the eprom as that code was nowhere to be found. I've also got code I tweaked just a bit for Mike Riccio when he was having problems booting his Geneve if you have problems assembling. The code I have looked like someone started to add separately a menu system similar to what Tony finished. I am not sure of the origin of that code and I think it is ignored.
I'm about 99% sure the swan image source code is based upon the Myart image code. That code can either be derived from the Myart source code, or if you look in the mame.zip file above under the BIBLE directory, I use code to load Myart images into that program. It's been awhile since I looked at the Myart image code, however there are two image formats depending upon whether one was using 16 or 256 color. The Myart picture code should also be able to be found in ABASIC in one of the source files.
Just a head's up for anyone wanting to use the code with a GenMod system. There is code to test memory that tests memory pages from >00 to >3F. The original 0.98 Memex mode eprom code changed the page scanning range to either >39 or >38. You had to avoid scanning page >3A as that would generate an error and not allow the system to boot.
Let me know if you have any questions. I did just a little bit of tweaking on my end a couple months ago on a separate system, and I know I have code that assembles and runs.