I also vote for having it welded with it on the sled. I had to change mine when a connecting rod broke,smashed thru the engine block and punctured the exchanger. I think it would be hard, but not impossible to change it with the engine in place. There are about 18 rivets to drill or grind, plus a few extras that get in the way when you pull it down and back into the tunnel. The chaincase has to come off to remove the drive axle. The long rear motor mount bolt has to come out because the exchanger has 2 "ears" on the sides at the top that the bolt passes thru. The hoses are a real tight fit, especially the short one on the right. That's only half the battle. It takes alot of prying, tapping and cussing to get it back in and all hooked up. It's not fun.