"I'd like to the keep the rear that it has (it's not a torque tube style) but simply convert it to 6 lug"
There's no way to convert that rear to six lug. A six lug wheel won't even fit over that full floating hub, if you're thinking of re-drilling the bolt pattern.
If you want a six lug rear, I think the easiest swap may be a 1/2 ton Task Force series rear. I have a '55 1/2 ton rear end kicking around the garage and the spring pad spacing is very close to my '52 3600. Within a half inch I believe. I considered the swap myself at one time.
