GURPS DF came about not out of an attempt to duplicate the feel of D&D 4 E, but to garner the feel of an Old School Dungeon Crawl. in effect, as part of the same nostalgic wave that drove the OSR, coupled with the sense that gaming as one remembered could be done with a better or simpler system, that also generated Pathfinder.
The best tonal conversions are not translations, but reimaginings. I own not only a vast amount of DF related games, but also a huge amount of pdf material given free by the publishers of the OSR. BlueHolme, Labyrinth Lord, BRG, Dark Dungeons… and Swords & Wizardry. I have the electronic versions of the Whitebox, Core and Complete rules, and many adventures and supplements. They are pretty awesome, having a great graphical feel. The Complete rules have a bold cover that immediately brings to mind the Erol Otus magenta box cover. That was the game that first brought me in, so many years ago. The play is smooth, the prose evocative, and Fog God Games did a great job; you can get
the Complete rules from them here;
S&W Core and White box rules are available from Mythmere Games.