I've posted before about using A1 Slave Pits of the Undercity in GURPS.
I've done it before.
But how would it be for GURPS DF?
Let's take a look.
Numbers mean much more in GURPS than in AD&D. Being outnumbered 2:1 in a close-in melee in AD&D sucks. In GURPS, it's quite likely lethal. Fighting foes with cover, waiting in ambush, and being forced to come out of a tunnel/funnel into a large combat area is rough at best. In AD&D, it's just spice to the encounter. While DF adventurers are far tougher than the low-to-mid level AD&D guys suggested for the adventure, the foes equally have more options.
Overall I'd say it's a wash, with a slight edge toward more dangerous foes at numbers tough to deal with in GURPS.
The enemies in this adventure are relatively low-powered for DF. They're numerous, see above, but they aren't terribly tough. Some of them can be, depending on how you stat up the Aspis, what spells you give the clerics, and so on. Setting the bosses up to at least 250 and more like 300-375 points might make them a better challenge for a medium-sized DF group. Still, it'll be critical hits and player mistakes that cost DFers in a way that they'd never cost AD&Ders.
Traps and Obstacles
The access to spells in GURPS on a routine basis means most of the obstacles are more pass/fail - if you have the right spells, you'll pass them easily, If not, you'll fail to pass them easily and need to do some thinking like the AD&Ders do.
Traps have the same situation. They're going to have much more potential lethality in GURPS but likely fail due to spells, armor, skills, and defenses. Player prep will have an amplified effect due to those.
A1 is a pretty good target for a DF conversion. Adding a real heavy-hitter monster or two might add to the challenge even if it takes away from the purity of the conversion. All in all, I've run it GURPS and it went well, so there is no reason it can't be run in GURPS DF despite the presence of stronger PCs in general.