how to spider gears

I have a 7 1/4 rear end with broken spider gears out of a 73 dart which has the large lug bolt pattern. I also have a 7 1/4 with the small bolt pattern. I need to know can I just change the spider gears from one to the other will they interchange. Can I do this with out pulling the hole third member out of the housing Also one is a sure grip the other isn't. Thanks