Big dead blow hammer.... there is usually a guide pin on it for orientation so it won't fold back at 90degrees for ya... here's what a fellow CB member wrote up...
" Re:dana 20 removal/installation
i just took mine out saturday actually, and put it back in sunday, i had to take both driveshafts out, get something to hold up the tranny, then take out the cross member, after that you just have to look over all your shift linkages and make sure nothing is connected to it still, then take out your speedo cable, now it is ready to come out, you just unbolt the case from the tranny adapter. and it will pull off, it wont fall off because it fits back on a little pin and on a gear, when you slide it back off one of the gears will still be in the adapter, you will have to take a snap ring off to pull that off of the output shaft, its really pretty easy, everything just bolts up and you will be able to see pretty easily how to take everything off, but going in that order made it really easy for me, but watch out when you get that thing off the adapter cause its pretty heavy. Hope that helps, if you have anymore questions just ask my knowledge of it is really fresh right now."
GOOD LUCK