What size truck are we talking about here?
IIRC, the 3100's took 6 lug wheels, the 3600's took 8 lug wheels. I'm not sure about the bigger ones, but I think that the 3800's took 8 luggers too.
I have never heard of adapter plates for the hubs to take them down to a 5 lug pattern. (It doesn't mean that they don't exist, it just means that I'm running my stock wheels)
I'm thinking that you'd have to gank the hubs and drums and replace them with the five lug equivalents.
And if you're going to do that, you may as well redo the rest of the brake system as well, because chances are the shoes won't fit the new drums.
You could just get new rims that fit your lug and hub pattern. They make them in pretty patterns and colors.
