There are no pre-made dual exhaust kits for an 89 Ford van. I also have an 89 Ford and have looked for a dual exhaust kit for years.
You can get long tube headers from Hooker (shop Summit racing) or Hedman (shop JC Whitney), but everything behind the headers is a custom job. Keep in mind that if you are running the factory fuel injection the headers dont have an O2 sensor bung and adding headers might mess with the computer’s calculations for fuel injection.
If you don’t have to have dual exhaust you can just run a larger single exhaust. The factory 2 1/4 pipes coming off the manifolds going into a single 2 1/2 pipe would be fine.
Honestly, I don’t think the SVT Cobra motor will be a good choice for a swap. The stock exhaust manifolds are different than the van manifolds so unless you install headers on the van you would have to change at least the head pipes when you swap motors.
Further, vans need torque, not high rpm horsepower. If I was going through the trouble of an engine swap, I would go to a warmed up 351W or even a 300 six cylinder over a 302. Or maybe a 460 or diesel, but those are more involved swaps.