Go over to the Medium Format forum on photo.net..On the right hand side of the page go down to the Pentax 67 Lenses sub-forum..You will find many threads on the Takumar 300mm f4 lens..As I recall, the main problem with that lens is its lack of a tripod mount..Any kind of homemade mount that clamps around the body of the lens is going to help, as then one can use a Bogen 359 Long Lens Support on the camera, and mount the lens to the tripod..Which will make things much steadier..The Takumar 300mm f4 lens is a lot of weight, 1425g, to be hanging out off of the lens mount of the camera unsupported..
Medium Format Photography forum from Photo.net -- Pentax 67 Lenses Manfrotto by Bogen Imaging | 359 Long Lens Support | 359 | B&H