I think you have a
lot more research to do if your plan is to install a water-cooled Porsche engine in an air-cooled chassis. From all I've read it is a
significantly involved swap. There isn't really a way to adapt one to a 915 or G50 transmission, and there is no room for a later transmission without a ton of cutting.
An LS swap would be much simpler (as there are sorted kits available), and you'd wind up with over 400 cheap horsepower. An air-cooled 3.6 swap would have a much higher parts cost, but is almost drop-in simple in comparison to any water-cooled swap.
Cooling is low on your list of concerns for a swap like this, so I would spend more time getting the drivetrain sorted 100%. With the number of monster air-cooled race motors in some of these cars, and the existence of a well-regard kit for water-cooled motors...this is pretty much a solved problem without having to do all the customization you're proposing.
If you're still goin'...:
Most ducting I've seen goes into the frunk area then
down out of the floor in front of the gas tank. For what it's worth, my '84 with a '95 3.6 had a center-mounted oil cooler with
no ducting, no hole behind it, and nowhere for the air to reeeally go and was raced in this configuration (fanless Carrera cooler in the right fender and a center cooler) by the previous owner and he said he had no trouble with excess heat. The bumper/valance was a '73 RS style:
Here is a thread for a car with a Renegade Hybrids setup for a Chevy LS that has substantial ducting for a radiator up front:
RSR LS Conversion
