Jed,
I'd still advise looking for a 2 barrel carb rated at 500cfm, which is what you'd use with a 4 barrel. I don't have a specific reference but they are available. Remember that most 318's and many 340's and 360 engines also had 2 barrels stock. Also, 2 barrels are easier to rebuild, but I'd look for a new one that is tunable. It might be just as expensive as a 4 barrel however.
There are also other things that you can easily do to your engine to help: dual exhaust, blocking off the exhaust heat riser into the intake manifold, going to electric or mechanical choke, and making sure that the distributor is set and timed right and of course correct valve settings (very important with solid lifters).
What problems did you have with your 2 barrel carbs?
