Dirk used an m58 helical and a Contax 21mm finder which provides around the same view for a 65 mm lens in 6x12 format. He also mentioned the details of calibrating the helical and that information could be very helpful for a beginner engaged in camera making.
You can find the details of the construction of this camera in Dirk Fletcher's blog post. Dirk has made many panoramic and other cameras over the years and his posts are laden with construction details which can immensely help a novice and as well as an expert in this field.
Detailed and close-up pictures of his handmade cameras can be found in his Flickr Gallery.