Geo H Thomas published a design for a boring head in the Model Engineer circa late '70's, sorry don't have reference handy. It will also appear in one or other of his published books of workshop tool designs. I think that Hemmingway market a material pack for this design, but it can be made from suitable steel sections in any case. GHT went into very helpful blow by blow detail of the machining sequence and process to make this 'head in his articles, very helpful to many builders. This is my example which has been most useful to me over the years. Dave