I am just finishing the installation of 4 speed muncie conversion in my 68. I used the location of the 4 speed console shift plate to cut out the hole in the tunnel. I am not sure what you mean by 4 speed tunnel hump. It's pretty much just a hole in the right place for the stick to come through in the right position for the console. I had a regular hurst comp plus set-up but that meant one had to cut the console plate to stop it from hitting. I bit the bullet and ordered the correct one firebird one. I have never heard of someone setting up a muncie to shift backwards. I have a lot of pics here of the correct linkage set-up if that will help you at all.
http://www3.telus.net/public/68bird/transmission3.htm