8 1/4 or 8 3/4?

Hey guys I have a 340 scamp stock rear and looking to upgrade. Has 340 with rpm eddy heads 800 ffm eddy carb air gap intake 3000 stall 727. It's a cruiser not a drag by any means and am looking to upgrade th rear. I haves 8 3/4 housing no gears. I found a 8 1/4 323 with posi for $400 complete drum to drum from a 73 dart my question is would it be better and cheaper to buy the complete 8 1/4 and sell the 8 3/4 housing or built the 8 3/4 ? Any ideas thanks guys