The guys are right about the old heads and imo unless you are trying to stay with completely vintage parts for show or go then it would behouve you to buy a set of aluminium heads bare. Then buy a cam kit of your choice where you can match the valves, springs, lifters, and cam with the heads. This will make your life so much better if you put together a system that has already been designed and works.
Check these links out:
COMP Cams K33-600-5 - COMP Cams Thumpr Hydraulic Flat Tappet Cam and Lifter Kits - Overview - SummitRacing.com
Edelbrock 61859 - Edelbrock Pro-Port Raw Ford FE Cylinder Heads - Overview - SummitRacing.com
COMP Cams 1046-KIT - COMP Cams Ford FE Shaft Rockers - Overview - SummitRacing.com
Let your machinist put this together for you unless you can check you spring rates etc. Let him (if he is quailified) chose the right length push rods and valves. He can probably flow test your heads too. Once your heads are built and tested the install is simple and you know you have a matched set that works well with one another. I ran this exact set up in my cobra for years with a nice Quick Time 780 Carb and Performenr RPM intake. Nice little rumpty rump and power when you want it. If gas mileage is important to you .... disregard the above.
