I'm sure you're aware that I hold the distinction of making this site create a Lynx category in the Hacks section, as I was the first to submit a hack.
However, that was a relatively straightforward assembly hack. I didn't touch the graphics at all, so I've no idea what the graphical situation is with the Lynx.
I would suggest that you open the ROM in Tile Molester and see if you can find anything resembling graphics. Problem is, even if you do, you'll have to deal with palettes and such. Frankly the best option, in my opinion, is to just play the game in an emulator like Bizhawk and save lots of screenshots, then work from them.
Perhaps going into the ROM might reveal level layouts but that would be pretty advanced work. I think screenshots and hard work are probably the easiest method, I'm afraid. Maybe someone else who has done such things before has an opinion, though?