Rear End Fitment on 64 GMC Pickup

My rear end is now a jigsaw puzzle and the axles look like they are worn too, so I'm looking for a complete rear end swap but have no idea what will fit my:
1964 GMC 1000 pickup (long bed) 6x5.5 lugs

Does anyone have any idea what I should be looking for? I would prefer to find something close to a 308 ratio to give it good manners on the highway, but I'll deal with whatever I can find that will work. I have leaf springs, but don't mind if I find coil over. We'll weld the tabs and make it work.

Could I get by with a shorter axle and find some bass ackwards 5 lug to 6 lug adapters that will extend them to the correct length with the wheels on? Since I want it geared tall, could I even use a car rear end? What are my options?

 

What is the width of your rear measuring from wheel mounting surface to wheel mounting surface ?

 

if you want to stay 6 lug, stay with a gmc 63-66 rear. the chevy uses traling arms while the gmc (as i remember) uses leaf springs. when i tore up the 12 bolt in my 63 chevy truck all i had was a 76 trans am rear end, it was a little narrower and i had to weld all the mounts on it but it works great. it also seems like the 67-72 truck rears are a little wider to. as for as gears the newer 12 bolt gears will interchange, but i don't remember if the gmc was a 12 bolt.

 

Best low buck swap with same 6 lug, and with finding good highway gears, is a 4X4 rear from a K10 pickup, blazer, or suburban from later 70s to mid 80s. They are the same style, starting in 73, but you will find more lower number ratio donor rears by getting into the late 70s at least. Earlier 70s gets 3.07 on average.

These rears will be 1.5 wider flange to flange, but that is not a problem because the original rears were narrow, and the tire is set way into the wheel wells, so 1.5 looks better.

Gears I have seen in later 70s are 2.76 on the lower numbers, and if you get into the 80s, I think 2.50-ish.

those later housings were recast to take the HUGE pinion on those low number sets, so you can't use an older 73 type housing and use those big pinions.

I'd use at least the 2.76 on highway on mostly non-mountain driving. 3.07 will still rev on highway speeds.

 

Thanks. I'm pretty married to my 6 lug to keep my wheels I put on there. They really make the car. The rear end that was on there wasn't stock. It was a Dana and measured 61" I had a pair of 2" wheel spacers on each side that brought the wheels about as close to the fender as you'd want to go, so say 65" total or a bit less.

Much appreciated.

 

1971 up until the late 90s 2wd used 5 bolts the 4x4 stayed with 6.