Easiest to put in is as stated earlier - put in a '65-67 10 bolt out of another Nova. It will have the 5 lug axles. a '64 would also work but if you ever want to upgrade to a Posi, you will need new axles too.
why not put in a rear end out of newer s 10 truck,blazer or gmc sonoma? They are 54" drum to drum 8.5 and you find them with different gear ratios posi and disk brakes. You may just have to move your perches ,but I'm not sure how much.I think this is what I'm gonna do.