A possible source for you would be Precision in Nevada, 702-263-6300 . They make the bronze guides that you see in seemingly all of the aftermarket aluminum heads.
They make severe duty stainless valves which are used by just about everyone (Edelbrock, AFR...pick your manufacturer, etc).
The only issue is that you need to establish a business account with them. That only takes a minimum order of $100.
These are the components that you want. Everyone just repackages their products and marks up the prices. All are made in the USA.
I don't have their web page link.
I have my own "valve job" equipment since there aren't many local shops that will do a real three angle valve cut. Some race teams go more angles then that but on a street car that is huge overkill.
Cleveland heads really respond well to a high quality valve job. They are worth the effort. Most aftermarket heads already have them and are using Precision's components. My AFR's came with a 5 angle out of the box and CNC ported.
Building your own can be fun but it is time consuming and if you had to pay someone to do it you would be triple the cost of buying an aftermarket head already to bolt on.
The Ford iron head pockets to me are controversial. They have cast in "reduction rings" just under the valves. Those were put in to increase throttle response on street cars like the Boss 302.
If you look at the cross section of the port in the Boss 302 competition booklet, "Off Highway" , I think that you will see that they recommended removing that ring for competition.
On a 300hp 351c on the street, especially with an automatic transmissioned car that is used as a commuter also, leave them in. In order to get the big numbered horse powered engines, you need to take them out. Then the heads start to flow ridiculously big numbers but you need to match them with a camshaft and that doesn't match rush hour bumper to bumper traffic characteristics at all.
It depends on what you want out of the car? I would think that there aren't many Panteras left that need to be worried about being used constantly in that type of traffic? The original equipment engine would still fit that bill.
The 351 Cleveland is pretty easy to get 500hp out of even with the original (worked) heads and in a Pantera with the short exhausts, make sound like a Formula 1 car bleeping the throttle.
It MIGHT be the safest bet to have an original set of iron street heads that you keep on the shelf and a nice set of aluminum high port heads to make this thing scream, and scream they do with relatively little effort.