Fox had just come out with the .29RC in 1972. SO it might look like this then.
more about them here
http://www.rcgroups.com/forums/showthread.php?t=1164366
I think the .29 wasn't as popular as the .36RC engine though, mainly people would tend to lean towards the larger displacement engine unless they had a competition event they were getting one for. But the .29 was, sort of, a hop up for a .20 size plane during that era.
