Ok....
Better question....
Anyone know who does good port work?
-beerjet-
I know a guy...

You can do and get quite a bit more than people give these heads credit for. In this day of being able to buy super rad big heads, a lot of folks just kinda dismiss what you can get away with on a gm casting. Granted, they lack on the exhaust side compared to aftermarket, but not enough to not consider them on a 500 inch big block. The stud conversion really depends on what you're going to do with the thing, what sort of rpm and spring pressures. Flat tappets and typically a hydraulic roller or small solid roller will be fine with the conversion studs in a typical river boat . Something that is going to see rpm and or run a decent sized solid roller with stout springs to match... then even machining to accept the 7/16-7/16 studs is really not a big deal... I do it all the time as using the seat and guide machine makes it a snap. Port work is gonna be something that you're going to want to do to get what you can afford out of these heads. Cheap, easy way to get some flow improvement and lighten your valve train and also broaden your selection of valves is to install 11/32 valves either by going with .342 id bronze guides or installing guide liners in the existing iron guides (depending on how "inexpensive" you wish to go) You're gonna need valves anyway, might as well as get something that's gonna kill two birds with one stone. Obviously, the best way to achieve the clearance and finish you want will be to hone to size, which we do on ALL guides. Depending on what fuel you plan on running, a good set of hardened exhaust seats if you plan on running unleaded. Open the intake up to 2.25 and stick with the 1.88 exhaust. You will want at a minimum a decent valve job and all you valve heights exactly the same (so all your geometry will actually all be the same), and chambers all the same (you'd be amazed at how far this stuff can be off , even done by "professionals")
Basically, it all really boils down to your budget to requirement ratio... you can go full on double throw me down racey and spend quite a bit... or go bare bones stock and spend a little. A little more info as far as what your trying to do with this build would dictate the demands on the cylinder heads, and where the best bang for your buck will be spent.