The 5 lugs are going to be the smaller 5-on-4 3/4" pattern, I believe. Not certain, but I think that's what the cars use. Trucks use 5-on-5".
Aside from that...400hp in a truck, well, are you going to have traction? If yes...I wouldn't be so sure. In the 3400lb F-body, in about 30-50 more hp with traction, they start having problems. A 4000lb truck with traction might be too much.
But if you don't run slicks and let the tires go before the rearend, you should be fine.
