The lift from an over under kit like the part # K71-385-00 that you referenced gives you a lift of the diameter of the axle plus the thickness of the leaf spring pack. Since this is for a 3 inch axle it would be 3 inches plus the leaf spring thickness. Most likely around 6 inches. view full answer...
I went out to the warehouse and measured the mounting plate of the Ultra-Fab 2" Trailer Hitch Receiver for 5th Wheel Trailer Frames, # UF35-946403, you'd be welding. It is 4 inches wide, 3 inches tall, and 2 inches long. I've attached a picture to help. view full answer...