OK, I looked at your pics. Those cardboard fender liners would be better if they didn't go all the way to the firewall, there has to be somewhere for all that hot air to go. Louvers would work. Don't duct the heater plenum into the engine compartment. That's OK for carb air, but not enough flow for cooling. Besides, S10's don't have any way to shut off air flow through the heater duct, you'll get heat coming in all the time. If it's a fairweather cruiser you can delete the heater/AC, but in the real world, that ain't an option.