I left my original frame rails, i had to hammer, pry, and sort of reshape them to fit nicely in the bad dogs. I was not particularly easy, but it wasn't HARD. Just took my time with it and occasionally got a bigger hammer. I had my car up on a rotisserie and did not feel comfortable cutting the rails off without bracing it up first, which i suppose I could have done. I used tek screws, the self drill and self tapping kind. My biggest piece of advice is BEFORE you weld, get everything clean, flat, clamped, screwed and fitted up as near perfect as you can. The fit-up will not improve after you weld, really.