Kes Gaming YT

Yo!! It totally sucks you've got to replay those levels from DMINATO2.wad, but at least you can properly finish map 07 (and man I love the Wad Archive):

The button you press after the blue door opens the final door in the original version of this.  But as you know, whoever messed with this level is a douche.  

Near the southern part of the map is a bridge over the slime with a big pillar that lowers with some barons on it.  After you've cleared out the level and pressed the button after the blue door, come back over to here, stand on the lowered pillar and as it starts raising, jump north-east to the little platform that the button raised.  This will allow access to the button that opens the final door.  Very sneaky....

And also, I'm sure you know that map 08 is impossible to finish because the tag that lowers the walls only works in E1M8 of Doom 1.  That's a LOT of aracnotrons and cybers, man....