[me and my metro]

Like Oil Pan 4 says it is a no gain ratio wise. Actually you will turn slightly higher rpm on the highway. Did your van ever come with a standard transmission? Clutch pedal stuff may be a pain to fabricate.
Back in the early 80s manufacturers used car based transmissions with a flipped 3rd gear to get overdrive transmissions. If you are not going to work your van like a truck you might look at a v-8 car transmission. It would have 5 usable gears with good rpm splits.