I had a AWI 4 into 1 on my Superior IO-360 with horizontal induction. The fit was excellent and needed no modification to the exhaust airbox or cowling. Now the sound, I never personally heard it however I was told it has a much deeper throaty sound to it compared to Vettermans. And not that I need to say it bud man does it look good.
As far as the heater goes you have nothing to worry about, the welded screws do what they are designed for and work great, I was never able to pull the heater more than half open before roasting.
I no longer have the airplane but I can still answer any questions you might have