i was able to put the 28splines out of an 8" carrier into a 31 spline 9" carrier. so you should be able to get a 31 spline open diff and put you 8" spider/side gears into it to use with your 28 spline axles.
Any small to midsize Ford/Lincoln/Merc that had a leaf sprung rear. They all had the same 43" ctr to ctr leaf spring pads. A few may be wider than the Mav though (71-73 Stang)