I just did mine. I cut the rivet heads off with a torch and then I used a grinder to make sure there wasn't any part of the head left over. Drove them out with a hammer (the largest BFH you can use works best) I didn't drill a single rivet.
To remove the side plate that holds the tandem suspension, cut off the rivet heads and then use a coulpe chisels between the frame and plate, and it comes off fairly easy.
Same with the tandem suspension mount. Take out any bolts that hold it on and then cut off the remaining rivet heads inside the frame rail, then use the same chisels to seperate the two, and they pull through the frame with the suspension. This way with the rivets gone you can bolt the crossmember back to the frame with bolts through the remaining rivet holes.
Most of the rivets you can leave right in the frame (side plate rivets for example). Just grind smooth with the frame once the plate is gone and call it good. That way it dosn't look all Swiss-Cheesy for no reason.