there's an old book series in Germany, the "Waffen Revue". I've googled for an index, found "8,6cm Raketenabschussgerät" and the direction to Waffen Revue Nr. 44, dated 1st quarter 1982. And this special booklet was bought via e-bay; 14.00 €.
There are not only the drawings, also the description/manual of the old and the new (M42) version and drawings and desription of the different projectiles (explosive, light and wire (40m or 100m long)).
PS.: I've sent the drawings and some pics to Cammetts, to challange their craftsmanship - I think Robin Carpenter was very interested!