There are a lot of posts here about this bike. This is the most complete, and probably the most positive:
http://www.bikeforums.net/showthread...ght=gmc+denali

I worked on a few of these back in my wrench days, and these are my thoughts:

• They are heavy. Like almost old schwinn heavy.
• The shifters are insane, and you probably aren't going to be able to get them off.
• It might actually have horizontal dropouts, but I don't remember for sure.
• All the ones I saw were set up horribly. This is more a reflection on Box stores' build quality, but still. When the bike is set up so the break pads are missing the rim (you read that correctly), it still sort of influences your opinion of the bike.
• Many old 10 or 12 speeds have better quality. I won't say "most" old bikes are better, because I think people underestimate how many junk old bikes are out there. However, I will say any old bike will hold its value better. An 80's road bike isn't going to depreciate any more than it already has.

Point is, there is virtually no way I would get one of these. That is a probably a little harsh, but if I saw one of these on CL for $30 and an old Fuji on CL for $30, I would go for the Fuji almost every time (assuming the frame is not crap). While the shifters are the most glaring example, there is just a lot of junky weird stuff they did on this bike that I would not want to deal with converting. If the dropouts are vertical, that would seal the deal for staying away from this thing.