Usually a chassis is the previous model year from the Roadtrek "coach"
the dodge VIN will have all the info on the motor etc, ask the seller to provide both vins and just google the dodge vin code.
it'll give you info on the motor, build plant, sequential and birthdate.
wacky sellers fall into 2 groups: scammers and confused.
walking them through a process will tell you which you are dealing with- the confused can "forget" that there is a 4 foot rust hole in the floor- you have to be careful.
Usually an OD tranny will have a big "O" icon on the shifter ( instead of D for Drive) followed by a 3,2,1, a 3 spd will be D, 2, 1
ask for a pic of the cluster, that may tell you
according the Dodge the following were available in the 1996 2500:
Available Engines:
220-hp, 5.2-liter V-8 (regular gas)
175-hp, 3.9-liter V-6 (regular gas)
230-hp, 5.9-liter V-8 (regular gas)
Transmissions:
3-speed automatic
4-speed automatic w/OD
mike