The canton tray is full length and in my opinion better then the original tray. It does need some filing here and there to work correctly with the oil pick-up tube bracket and the block.
The sealing issues come from places where oil can sit on top of the tray and find a way to the outside of the block under crankcase pressure. Once the weak spot is breached, it only gets bigger. Having everything clean and free of oil, a stud kit to line up and assemble the pan and tray, and the engine being out and upside-down really helps sealing. I don't know if you could ever get it right trying to do it under the car with an oily engine.