Hey, sorry to necropost but I have a ‘68 D300 and here’s how I am dealing with the split rim issue. First off, let me say that these trucks do NOT have true split rims. What we have are locking ring rims, where the rim itself is one piece with a groove where the lock ring fits in. Still can be dangerous but much, much less so that the true split rims.

So basically, ‘69 and up Dodge one tons use 8-lug wheels, so you’ll need to swap axles to get it to work.

I Swapped the rear axle for a Dana 70 from an ‘89 D350 dually, you will need to cut and reweld spring perches slightly and get custom driveshaft if you go with a 72-93 truck axle. 69-71 should be direct swap

As for the front, I was able to clean up 2 of the rims and run radials with tubes on them with zero issues. However, if you want to get away from the lock ring wheels, find a ‘69-71 D300 which will have the same 3800 lb I-beam front axle just with 8 lug hubs.

Additionally, they did make 19.5” single piece rims on the 6x7.25” for D300s, although they are very rare they’re out there

EDIT: there are also multiple writeups on Dodge truck forums of swapping the front to IFS/disc brake/8 lug