There probably isn't a single anybody that makes a lift kit for a minivan outside of retrofitters that lift rear axles for paratransit vehicles. Most of them won't change the suspension geometry any more than they have to either. You're probably going to be entirely on your own fabricating parts to lift it.
See what the difference in spring heights between engine sizes. the heavier engines may use a beefier spring, But if you already have the large engine, it's all custom work from there, It'll be going to the scrap yards and finding springs that are similar thickness and design and hope you find something that's taller.
Air bags maybe your only other alternative