Already cut one hole in wing next to exhaust, I don't really want to put one in the other wing as I plan to duct incoming cold air at the carbs and then let it get sucked out of the opposite side of the car to keep the engine bay nice and cool.

size of current outlet approx 4x7 inch, inlet above raditor 22x2inch. I'm planning on ducting the raditor out to the wheel arches.

I've also started to make the panels for the underside of the engine bay.

Will having only one side vent affect vehicle stability at speed? or will it not really be noticable.

cheers

You would have to move a hell of a lot of air to affect stability at speeds under 200 mph. I reckon you will be fine

sounds good to me.