It sounds like a survivor car. That prompts me to say keep it original.
If you are going to be driving the car regularly then it makes sense to use a higher performance head.
Before you put a nickel into your iron heads, get a written quote. Then you will be able to make comparisons. As neither of the heads you own have hardened valve seats, maybe the cost of that should be included.
The main problem with aftermarket heads seems to be too little clearance between valve and guide. Correcting that takes a machinist or adding to your tool chest.
If your estimate is over $1000 your decision is made for you.
Here are two choices:
1. The Sidewinder head as sold by Moparts Racing, owned by Todd Marsh, known here as Sasquatch. Contrary to what some are saying, this is a Chinese head you can run right out of the box, For $895 you get a pair of bare heads and valves. Then you consult with Moparts Racing for spring, retainer and keeper packages. They get assembled with discrepancies corrected, then ship to you.
http://mopartsracing.com/parts/Sidewinder.htmlThis head casting is also available from ProMaxx, but it seems to be more expensive. I guess their profit margin is fatter..
2, If you must have an original looking head or are absolutely bucks down the Stealth head is the one. This head is delivered to your door for $1000 a pair. Literally hundreds have been run right out of the box without failure. Some have had the guides too tight to the point of sticking the valve. The heads are assembled with springs 130# on the seat and total allowable lift of 0.510. They use generic springs and retainers and Comp keepers.
I'd disassemble the heads and take them to a local machine shop, have them correct the guides, mark each valve to the hole it is for, correct any seat problems, and then I'd take the whole mess back home and assemble it. This head has been in production for around 10 years and early production issues have been dealt with.
http://store.440source.com/Stealth-Aluminum-Cylinder-Head-COMPLETE-SINGLE-HEAD/productinfo/200-1055/There are many better heads than these but they cost more and won't work any better on a street car. Either one unported is worth more than 500hp.