small block chevy 3973370 casting number. They have the double hump casting mark with the accessory holes. Just bought them off ebay to put on my truck. From what I can tell they have 1.94 intake and 1.50 exhaust.

 

3973370....69-70...350..........over the counter in US, Canadian 350/300hp production use in Pontiac, 64cc, straight or angle plug

http://www.mortec.com/castnum.htm

 

Not a production head but an over the counter replacement head for the 492. Everything mentioned above plus they have accessory bolt holes. They didn't come with 2.02/1.60 valves and they have press in studs. I didn't think they were available with angled plugs.

I ran a heavily modified set on my old 383 which ran high 11's until I threw a rod.

You can get the larger valves installed. Do some port work. Get the spring pockets enlarged for bigger valve springs. Get the stud boss machined off for screw in studs.

However if you do all that, you could end up spending more for those 35 year old heads than a set of new Darts which will still be better right out of the box.

 

Thanks for the info! I just wanted to make double sure I wasn't getting screwed since it was an ebay transaction and I couldn't identify the casting number.