I guess I should've added that my machine is a navistar powered machine. I'm not positive, but I think the newer cummins powered 1680s had a somewhat larger physical size pump. When you take out those 4 bolts in the pulley, the pulley and coupler slide on the pump shaft so you can get the new belt between the pto shaft and the pump shaft. The coupler is pushed into pilot hole in the pulley. I knew I had to send the pump in so I had my machine in the barn and took the side panel off to use a forklift to handle the pump. If there are any splines left on the shaft and you just need to finish something quick, I dont know for sure, but you may be able to just loosen the pump and somehow hold it out enough to get the old coupler out and the new one in. Thats just a gues though, so dont take it as a sure thing till you here from someone that has changed the coupler in the field. If you had the new coupler there you could get and idea of the space it will require to randr. Again, my navistar machine has hard plumbed pump so I had to take the lines off before anything else. If your pump is hose plumbed, you might be ok to try moving the pump outwards with the hoses still attatched. If you do try this, leave the top 2 bolts in to hold the pump up and dont unscrew the nuts too far or they'l work their way off when you're under it. That pump is really heavy and some of the machined surfaces are sharp so be carefull. Make sure you clean the area off with air or something first so nothing gets stuck between the new coupler and the pto shaft. Hopefully someone here will have more info on just doing the coupler than I have. And thats assumig the pump shaft still has anything to bite into.