OK feeling much better after a good nights sleep. So now heres the rest of the story...
For 72-93 D trucks and 73 up B vans there are essentially 2 front suspensions designs, light duty and heavy duty. For the sake of reference I'm going to referr to the HD as 4000# front end since that's what Dodge called it. Also I mentioned B vans and while there is a fair bit of interchangablity, there's plenty that doesn't swap. Regardless, the pattern is the same for both chassis.
Among the 2 suspension designs, there are also early and late style, biggest difference was a redesign of the steering circa 1978.
To dispell some myths, the badge on the truck is pretty much irrelevant to which suspension the truck is equipped with. Exception is that all 100,150 trucks came with the light duty front end. No need to have an axle that can suport 4000# in a vehicle with a GVW of 4500# 200/250 and 300/350 were a mixed bag though the 4000# setup was more common on the 300/350, standard with dual wheels.
The GVW sticker in the door jamb is also fairly irrelevant, factors such as tires and frame rails can impact that number. Meaning a ld front end truck can have the same FAWR as a 4000# truck. The underhood sticker if present seems to be more accurate.
Engine choice is also mostly a non factor with the exception of the Cummins trucks, all factory Cummins trucks had the 4000# axle.
So, other than these cases, how does one tell which front end you have? Basically if it's 5 lug wheels its ld. The other tick is the tie rods, ld had fairly short inner and outter tie rods with a long sleeve. In fact the inner and outter tie rods can be swapped as an assembly. Techincally the factory speced l/h threads for the inner ad r/h for the outter but it's common to find them the other way.
The 4000# axle has long inner tie rods, short outters and short sleeves, they can't be swapped end for end and on vans the inners are different drivers vs passenger side. All 4000# are 8 lug wheels, BUT not all 8 lugs are 4000#
There are some parts that can be swapped between ld and 4000#, but not much. Pitman arm and idler arms are about it, possibly strut rod bushings. Even the shocks are different lengths. That said, as complete* assemblies they can be swapped. *Complete would include the engine/suspension crossmember though most who swap from ld to 4000# simply drill out the holes for the lower control arm bushings, it's ahrder to go the other way.
I mentioned lug patterns, the ld has 3 availible: 5x4.5, 5x5.5, and 8x6.5 and most are one piece hub and rotor. The 4000# has a separte hub and rotor. As for swapability of the ld rotors, well that gets extremely murky as bearings are different and the catalogs aren't much help in discerning which is which. Bet the 8 lug ld rotors take a different spindle.
So whats this all mean to Wylie? well based on the info he's given I'm going to say he definitely has the ld front end with currently 5x4.5 lug pattern wheels. Yes the oddball disc brakes, likely car sourced (C body?) bet they're pin type calipers. That said, I wouldn't automatically call them inferior since they're car based, plenty of C bodies had GVW that rivaled pickups. That said, parts availiblity for his current setup is going to be tough and a swap to newer stuff would certainly be worthwhile. BTW the 3/4 ton rotors aren't that much bigger than the half ton parts at least in the 73 up trucks. I'd have to look them up but I believe the calipers swap between half and 3/4 and yes 74-78 C bodies. So even the 3/4 ton brakes are car based...
So for Wylie to get 8 lug rotors without a complete front end replacement he'd have to find a ld 8 lug truck and grab everything from the ball joints out. Ideally a pre 78 truck to match the steering design but he could likely just swap the steering arms to keep things happy.
A note on ball joints: the 4000# setup used the same ball joints throughout the run. The 4000# joints have larger studs. The ld used the same ball joints throughout their run with the exception of some early trucks that may have used a threaded in lower ball joint vs a pressed in. Threaded vs pressed i believe used the same size stud however.
Not yet asked but upgrading to 8 lug rears will net a huge increase in brake size, 12x2.5 or 12x3 vs his current 10" (most likely) The most practical way to upgrade the rear brakes is with a complete axle swap.
As an aside, Wylie, just how big a camper do you intend to tow? 8000-10000 pounds would be something in the 24-30 foot range. Not many vintage campers in that size range.
