I think the tranny would go long before a VW I4 bottom end.
These motors can make 500+ with the factory crank.
>

  The issue you would run into using a 300+hp turbo VW inline in a
van....it would be dicey, tapping that much horsepower and torque and then
go pushing such a big blocky heavy boxy vehicle at high speeds...  with a
motor designed to push a small light much more aerodynamic sedan.....My
guess is you'd be buying bottom ends more often than WBX
Headgaskets....grin.