ps.. pulling the pto on a 640 will drain both the rear end oil AND the hyds oil.. so drain them first.. or be ready to have near 4g pour out the pto hole.. depending on how full hyds sump is.
utf is fine for both .. or gear oil for rear.. and utf for hyds.
lastly. there is a seal in between rear and hyds. so when pulling the shaft and re-stabbing it.. be kinda carefull that you don't hog the seal out. it likely already leaks a lil.. but the less dapage to the lip the better.
if you have the new assembly it's a 4 bolt and new gasket, no sweat job, then refill both oil sumps.