I angle milled my C4s to the intakes being 11.75°, this made port straighter and the valve happier on the intake side. But what is my exhaust angle now? I never measured it, just worked on the port to get 185 out of a 1.58 valve. The angle mill was starting on the exhaust side of the head and milling it to straight edge on the deck. It raised the intake ports by angle, and I would be sure it altered the exhaust. I widened the ports and the turn into the chamber on the intake side and the intake was already worked wider in the pinch on the pushrods that got in the way. There used to angled stock style rockers, likely still are. I did pull one stud out of the rocker stand and helicoil it. there was some angling on the head bolts too. The intake worked out well, A Holley SD that already fit my modified heads, the valve cover rail was a little whopperjawed but easy to fix with thick gaskets and right stuff.
But I was just curious, I cant measure it. We angle milled SBC heads to 18° and since the ports are moving with the valve stem angles they did better, in fact if you got caught they put weight on you.
Answers? my email is billballingersr at att dot net. If you don't want to say anything here. At 11.75° and widening the ports and pinch at 2.055s it did 274@.525 280 at .540 and 285 at .600