The best oil fill funnel I have found to fit an IDI van (at least the older gen) is this style of DEF funnel. It's shape and width makes it ideal. I got mine from Walmart, but they may have stopped selling it?
Walmart link: https://www.walmart.com/ip/Hyper-Tough-DEF-Diesel-Exhaust-Fluid-funnel-10732WRHT/370116357
Other stores seem sell the same thing under different brands, such as...
FloTool from AutoZone: https://www.autozone.com/shop-and-garage-tools/funnel/p/flotool-diesel-exhaust-fluid-funnel/399486_0_0
Hopkins from Lowes: https://www.lowes.com/pd/Hopkins-DEF-Diesel-Exhaust-Fluid-Funnel/1002488184
