too bad you're not closer. my brother has a complete Turbo II engine from a Shelby Lancer just sitting on the engine stand in his garage. ran great when it was pulled too. but for a van i would definately go with a 2.5L. more low end torque due to longer stroke.
you can't turbocharge your existing engine (it'* not practical anyway) but finding a 2.5 Turbo I engine should be easy (i would go with '89+ engine only). just add an intercooler (like a BIG NPR!) and a Garrett T3 turbo from a Turbo II engine and you have yourself a 2.5 Turbo II
or hell, just slap a T3/T04E on there, add 3" mandrel bent exhaust, a Turbos Unleashed 3-bar cal and +40 injectors, then crank the boost to 20psi and run low 13s all day long. with slicks it could probably be in the 12s and it could be done sooo cheap and so easy to do.
the '89 & '90 Voyager/Caravan even came from the factory with Turbo/5-speed so you could make that van really fast and fun! however the A413 can be built up to handle the power just fine.
yeah i know, i'm just rambling, what can i say i'm an old school Turbo Dodge nut
it'* all my brother'* fault; he owns 3 of them and they are all faster than my two cars! i'll own another one someday.
good luck with the rest of the job!