[Dan Case]

I can not answer all your questions but some were available for Shelby American's Lemans effort in 1965. The combustion chambers are similar to what was later used for 351 Windsor engines. The engineering part number is cast into the head. (I'll try to attach a picture.) I have seen sets advertised for as much as $6,500 but they usually go for less on ebay®. A set sold in early 2004 on ebay for about $800 advertised as just 289 GT heads.

Vintage racers have been buying up these units as fast as they can because some vintage race organizations require correct "period" engine components.

Dan