67 chevy rear end ?

[npc1]

Ok like I have said before Im really new to the 67-72 chevy trucks. I have a 67 chevy swb everything is stock as far as suspension goes (still has 6 lug drums all the way around) Im going to install a drop member from Porterbuilt so Im going to change the front to 5 lug but my problem is the rear axle I can buy the gears and the posi for around 600 and I can buy new axles and drums for about 500 which is not bad I guess but Im thinking Id be better off finding a 73-87 rearend that already has the gears and is already 5 lug and then I will just add the posi to it. So basically I need to know if this is possible (in other words will the newer rearend fit) and if not what do I need to do? If someone can point me in the right direction or show me where to look I would greatly appriciate it. Thanks again.