running 3", be sure to definately get those poly mounts. 3" will bang on the floorboards even more. If i were u, i would tack weld everything, make sure it all fits good, then take it off the car, run a bead or 2, put it back on to make sure it didnt move or shift, then take it off and completely weld it.
if you have any questions, just let me know either on this thread or send me a PM. Before u paint it though, run it for a day or two, then check it. I have a several pin-hole spots in my weld where air leaks out that i have to reweld still