The vans are tight on engine compartment space, so highly unlikely any big block would fit, especially the older 383/413/440 ones.
We know that a 360 from back then would fit because they were an option for the vans, which is a big bonus in being able to get mounting pieces without doing all the fit and weld yourself. Even beyond the extra displacement, the 360 is a better engine for torque at low rpm because of it's small bore long stroke design. Some of the "magnum" engines in the pickups around 1990 were quite powerful. I think you can get full roller/lifter conversions for the 360 which allows a quite a bit more cam to be put in as lift, gaining power without raising the torque curve rpm much. I know from experience the small port size Magnum heads on a 360 can easily support 350hp with a little work.
Mopar Performance probably has a complete crate engine in a 360 bottom to top, either with carb or EFI. They may even have a high torque truck/towing version as IIRC the used to do them.
Putting in a fully modern engine like the new Hemi ones is a huge job in most vehicles as it would require a full reharnessing of all the engine controls and computers. I took a look at what it would take to put a new tech GM 6.0/6.2 into my 5.7 equipped 96 Buick Roadmaster, and figured I could do it, but even with a fully equipped shop, it would be more than I would consider it to be worth by a big amount.
Of course you would also need to change transmission if you go with a modern setup.
My guess is that a swap to "smiled on" 360 would be in the $5-10K even doing a lot of the work yourself, depending on how non stock you go. A change to a modern engine would be considerably more than that if you have to buy a bunch of labor to do it.