This guy on ebay has several types of heads to look at. Havent gotten any from him yet but do plan to buy one of his aluminum head sets.
These are a 400 a set ready to bolt on with 2.02 valves and fully machined and checked over. Edit: these are 76 cc you will probably want 64 cc heads. They sell those as well. In several different casting numbers.
Performance 327 350 400 Chevy Cylinder Heads 882 SBC Bronze Guides 500 Springs | eBay
Plan on using an after market cam and lifter kit as well. You should be good for a few ponies. If you look at edelbrocks site they have a kit for the chevy 350 that includes cam and everything. They can help you select cam and head type by comparing parts to see what is like the kits or in between the two kits they sell. One is 410 hp and the other is 330 i think but either way best to stay low on the range there. I mention this because there kits a re very repeat able and can usally work with any stock short block. Since they make it for mass market sale. Not the best but will bolt to any dam thng and work good enough.
Hope this helps.