7 1/4 worth rebuilding?

hi guys I was wondering if it worth rebuilding my 7 1/4 differential it is an open diff with 276 gears it's making a humming noise while driving it it's in my 1970 Plymouth duster with a stock 360 727 trans and if it is worth rebuilding can I put the bigger bolt pattern axles in it? And can I convert it to posi?