[Pvmt-Pndr]

Honestly for either of your applications king pin or ball joints don't matter just about any version of it will work great... the main reason the off road wants the kingpin D60 vs the ball joint is well it's a kingpin but aside from that there is a about 3 extra inches on the tube on the (78/79 Ford for sure) driver side between the pumpkin and the thingy that slips my mind currently. That added 3" or so makes it a lot easier to run a 4 link setup. Later king pin models had the leaf spring mounts cast into the pumpkin. Which eats up the 3" or so on the tube. This is the version I had and it was a royal pain to work around when building a 4 link

We all know how ball joints are. Get a cheap set... well they're going to last about as long as a cheap set should. Spend the money where you don't want to touch again for awhile.

I'll throw this in just because I haven't touched on it yet. If you go with a 78/79 Ford king pin it should be priced around $1000 average in my area on average with 4:10 gears this is the most expensive option from a private seller. All other versions the last I looked which has been a couple of years should be somewhere just over half of that, so $600 ish. Give or take a couple hundred. I waited a long time before I purchased my 1 tons and was able to find my D60 and a rear D70HD for $800 both with 4:10 gears. Personally I would pony up a little more money and go with the F350 axles from a super duty for the simple fact the rear will have disc brakes also. My D70HD came with drum brakes and I made my own brackets and mounting hardware and converted it to rear disc also. That didn't cost much because I'm a journeyman millwright who can build about anything out of metal and get paid to build it at work but I will say it was very time consuming.

The swap I did was a mid 80s D60 that I have no idea what it was out of (I ran the numbers). The chassis I was using was a 1989 econoline 2wd that already had coil springs. I just made some not so fancy mounts on the axle and called it good. Oh and the best part was I slapped a 1953 willys truck on the frame with the 460 under the hood!! I did end up having to move a lot of things around with the suspension multiple times until I got it right though.

Now if either of you do go with a 2001-2004 D60 make sure it is in fact a D60!! You don't want to pay D60 money for a D50! They are identical from the ball joints out.

As far as the duramax/Allison goes I wouldn't throw the idea out the window about a set of 4:30s. You haven't said what size tires you are planning to run. Is the Allison 5 or 6 speed? I had a Cummins with a 6 speed auto on 35, 31s and 33" tires with 4:10 gears and it was an awesome combination for everything even with the 3 different sizes I ran. Plenty of gearing down low to get moving in a hurry (600hp) and the double OD had it running around 1400/1600 rpm at 60-70 ish.

Do your homework beyond me also guys. I'm not what I would call an expert I've just played around with what you guys are hitting on a lot of seems like and have done a lot of research myself. I'll keep answering any questions you have to the best of my knowledge though. Hell I might even post a picture of the Willy I was building if anyone wants to see it. It was a dedicated mud truck that I never finished because someone gave me enough money I would have been dumb to say no to.