RE: Extra 260 manual
I believe what you have is the Extra 230 33% with a 96 inch span designed by Jim Van Loo The 260 was derived from the 230 by going from a 4 to 6 cylinder and adding carbon on the ailerons along with other refinements. If so the original appeared in a construction article in Model Aviation in May 1986. It was latter kitted by Extra RC, then Ace took it over. There is a material substitution of the Mahogany (wonder if they specified night cutting) to spruce. Also the canopy mounts a little differently.
The magazine is available online at the AMA website for members. There are a lot of pictures along with plans in the article. There might of been a 260 design later also.