Should be listed on the drivers door post.
5X4.5"
15"
Your D100 came with a 8 1/4 axle
It is either a 22 or 30 gallon tank.
The manual for mine says 22 gallons or optional 30 gallons.
Factory equipped tire size will be indicated on driver's door jamb sticker. My '85 d100's sticker says the size is 205/75/15. 235/75r15 will work with almost no difference on speedo gauge
I have a 73 Power Wagon D-100 stock it will fit 31x10.50 but I tubbed mine and I can cram in 33x12.50
17 inch
The nut size of the dodge RAM is 11/16th. This is mainly for the 12th point of the 1998 model of the 1500 from wheel.
19 inch
14" wheel.
1 1/2