Giving prices is tough but I can say that matching pairs are fetching $1,500-$2,000. (sometimes higher too)
Since yours don't match, you can lower those figures some. (unless you happen to find someone with another mis-matched pair. In that case, they'd be worth alot to that person.
If I had these heads, I'd put them on ebay and sell them in seperate auctions. (make mention of each other in the description incase someone wanted the pair) From what I've seen, no 409 parts leave ebay without the seller getting a very nice price. (sometimes an outragious price!) I'd bet they do very well being hi-po heads.
I think someone on this board was looking for just 1 head a while back. I would think there should be a few out there looking for just 1.
Hope this helps,