Pick up a copy of Harry Higleys' book "BIPES". You should be able to find it at your local hobby store. The book features the Goldberg Ultimate for a large part of the building process. Included is a modification for the cabane mount areas. Costs around 12-$15.00.

There's lots of other information in there that will help you build your bipe correctly, and that can be used on other types of planes.

You won't be dissapointed.