dash vent covers

Hi all
I hope this is in the proper section
We have a 68 cuda that was a race car it has a 440 with fender well headers
I plan on driving this car on the street so I have started rewiring the car
The car has no heating or ducting we are planning on installing a small electric hot rod heater
But my issue should we cover the 2 upper dash vent holes or is there a vent system that would be best to use
Thanks for ur help