Howdy Back 4-5 Mustang:
Shrouding is not an issue on the exhaust side. The exhaust gases are being forced out of the cylinder in a high pressure, explosion-like environment, so shrouding is not a problem. Shrouding is an intake problem, especially if you were to attempt to use an intake valve bigger than a stock, late model, 1.75" diameter head valve.
The machining of the valve seats as Bill described will get the most in valve airflow.
The Clay Smith cam is right in the same camp as the others. Be sure to compare the @ .050" lift specs as well. As BIll alluded to, there is more to cam lobe design than the numbers. If you think of the cam lobe as an oval egg shape, then note that some eggs are more pointy while other a more round. Modern cam lobe designs tend to be more round. In this case the .050" spec will be a higher number. That gets the valves opening quicker and staying open longer through the opening and closing cycles. It pays to study, compare and shop.
On the valve lift question, more is not always better. I prefer to get valve lift from the cam, using a stock type adjustable rocker arm for a street type engine. There are several reasons for my preference. High lift rocker arms may be a good way to get more lift from a stock type cam, but they do add to side loading the valve as well as adding stress and possibly coil bind to the valve springs. If I were spending that kind of money for a rocker arm upgrade I'd be looking at roller tip rockers. The roller tip reduces side load and friction. Finally, going from a 1.5:1 rocker to a 1.6:1 rocker arm will only add approximately .030" lift to the valves while adding stress to the rocker and shaft. PS- be sure to thoroughly clean the inside of your rocker arm shaft in the course of your rebuild.
Lastly, your carb choice may be a limiting factor in your engine project. Which Weber is the one you are using? Is it a staged or staggered opening type? What is it's total cfm flow rating? Direct mounting will help it. But, I would suggest that you build your carb mount so that you will have the option of a carb capable of more performance. And yes, rejetting, as part of the tune, will be likely with your new engine.
Good luck and, again, keep it coming.
Adios, David