I've run across a pair of big block 291 heads dated June 1969. They are square port, closed chamber and use the "peanut" spark plugs and look to be in good condition. About how much are they worth? I'd like to make an offer on them before they are gone.

Depends on a lot of factors.
Are they freshly rebuilt, have they been angle-milled, are the valves oversize, how much porting and polishing???

Nothing special has been done to them other than maybe a valve job. They are just a used set of stock heads that were pulled off an engine..

No one have a guess?

If they need work to go back on a motor $800 - $1200
If they are done and nice and can be installed on an engine $1750- $2250

These heads typically bring good money because of what they were used on, L78's and LS 6's. Some of the date codes on these heads make them more desireable to a person looking for a set within a certain time frame. These heads being June of 69 may limit their worth to a 69 guy and may be too early for a 70 guy. Unless your building a period correct motor, I wouldn't spend too much on them. I'm sure there are other heads for cheaper money that will do the job. As far as worth, Jim's numbers above look about right.