I'm sorry, I'm not really a speedrunner myself,... but I believe to point of doing speedruns is to try and set a faster time than other people. To do so, you have to play the same game as other people, and KeeperFX is not the same game as Dungeon Keeper, even with the maps restored to original.
What I mean with frankenstein-version, is that you take bits and pieces from different games, in your case the game logic and balance from keeperfx, with maps from dungeon keeper. You'll get a working game, but it plays differently from both the original game AND keeperfx. So if you set a time on your speedrun, you can't really compare it to anybody else's.
To get KeeperFX unofficial to work, simply download it from the link above and
install it like you would the old version of KeeperFX. You could either extract the files from unofficial over the gog-folder you've already got in your screenshot above, or extract the files to a new folder, and use the launcher, press the 'installation' button and point to that gog folder to get two running copies of the game.
I don't know what you're saying exactly, but if it's about how to get the original maps in your game, you can do whatever, the original maps are in the package you download from gog.com, paste them in your keeperfx levels folder to get them into keeperfx. Whatever way you do is fine. If you're still online now, and have more questions, we can use the keeperklan chat box as well.
Here:
levels.zip