What is the length of the oil dipstick on a1994 Dodge B350 van with a 318 engine

I have to be honest, I'm not sure of anyone who will have data to share that will give you a length. It is not a recorded specification in any published manual that I am aware of. Best thing to do is find another vehicle local to you somehow and figure it out. Alternatively, create your own by performing an oil and filter change, adding the exact amount of oil required (this engine requires 5 quarts including the filter), let the oil settle, and then find a dipstick that will at least fit. Create your "full" line from where the level is. You will know for certain a proper "full" level having just performed the service.

https://www.ebay.com/itm/OEM-53020616AB-Gas-Engine-Oil-Dipstick-for-94-96-Dodge-Ram-Dakota-5-2L-5-9L-New-/371341351906