Kle, here are the factory issue specs.
D100 were ALL 5 lug, tubeless 15" wheels from 61-71. There was an optional 16" tubeless 5 lug wheel available by special order. Rare as hell and I've never seen one. These were NOT split rim.
D200 61-71, W200 61-71 and W100 61-68 were ALL 8 lug wheels, and if 16" they were split rim.
W100 69-71 were ALL 5 lug tubeless 16" or 16.5" This 5 lug pattern was an inch bigger dia than the D100 5 lug wheels.
16" 6 lug split rims were ONLY used 61-68 on D/W 300 trucks.
Your truck had to have been a 200 if it had split rims. No 100 ever had split rims.
Ive driven swepts daily since 1978, from Canada to Mexico and California to Michigan.
Ive photographed hundreds of them and stripped dozens in wrecking yards. Here is a partial list of what I own or owned:
61 D100 392 hemi project
62 W300
62 D400 dumper parts truck
63 D100 parts truck
63 D200 Crew Ute 413 NP420 parts truck
64 D100 Ute
64 D100 CSS Ute
65 D100 CSS Ute
66 D100 CTD NV4500 Daily Driver
66 D300 parts truck
66 W300 parts truck
66 W500
66 W500 parts truck
67 D200 CS parts truck
67 C500
67 D500 chassis/flatbed
68 D100 Adventure 383 727 parts truck
68 W200
68 D400 parts truck
69 D200 parts truck
69 D300 long chassis
69 W300 parts truck
69 D400 dumper
70 D100 parts truck
70 D200 CS parts truck
70 W100 383 NP445
70 W200 318 NP435
70 W200 383 NP435
70 W200 Crew 383 NP445 parts truck
70 W300 parts truck
70 W500 parts truck
71 D100 parts truck
71 D100 Adventurer
71 D200 CS
71 D200 CS Adventurer parts truck
71 W300 rock crawler project

Plastic trucks suck...
Iron trucks rule...