Bigdogge made a few tandem axle trucks, here's a picture of his Shockwave replica...
pic. If you take a look at the trk file you can see how it was done. The only problem with this is that when you turn the tires will overlap, but it's just a visual thing as the truck handles just fine.
> What sort of problems would I run into if I lengthened the frame?
Depends on how long you go. if just a couple feet then you won't even notice much change in the handling.
> Height might be an issue also...
Same as above except height seems to be a bit more sensitive to handling making the truck top heavy and tip-easy.
As far as scrape points go, yes they can be fudged manually in the trk so you won't hit any underpasses :o).. That was a concern of mine when I did the radio flyer with it's handle sticking up pretty high, but I was able to keep the points as they should be so I doubt it will be much of a concern for a 'normal' lifted truck.
