I would ask around and find a good, reputable cylinder head or machine shop and have them do a 3 angle valve job. Many will back cut the stock valves for the price of the valve job. This should cost between $100 and $250 total, more if they put in new valve guides or resurface things. They can magnaflux the heads to make sure you won't be porting a cracked head.
If the machine shop asks, you want:
1. Backcut intake valves:
1.77" intake valves will cost about $250 more than having the stock valves back-cut (between valves and machine work) for only 3% more flow at high valve lifts.
2. A Deep throat cut:
This will open the throat to its maximum and save some porting time.
From there you can carefully blend in the machine cuts into cast ports. It's very easy with a dremel and if you take your time, you won't mess up any of the machine work.
I recommend a dremel with a 1/4" round end double cut carbide burr because it is light and easy to handle and the burr will cut cast iron like butter. You want a double cut carbide burr, because a single cut burr makes tiny needle like shavings that stick in you skin and HURT. In comparison, you can practically swim in double cut shavings.
When you get the heads back from the machine shop, do the following:
1. Make the short side transitions into sweeping radii.
2. Smooth the roofs of the ports and the pocket around the valve guides (you only want to remove material from the roof and not take any material from floors past the shortside radii)
3. Smooth the intake pushrod pinch into a smooth curve.
4. Clean up casting flash in ports.
5. Match the ports to a gasket or manifold.
When you are done, the heads won't outflow a set of professional heads, but will flow way better than stock, with very little fear of hitting water.
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