Hi pro10is
apologies, late to the table, have to install 403 UL with ball mount. Different kayak, no flat surfaces to put the plate on the rails. Nobody sells ball mount - and yes, I checked you link to Murray Sports. Bought parts from Torqeedo, putting it together. In your opinion, strengthwise is it important to use the entire 40 cm length of the boom? Motor will be hanging off the side, there is no need to clear the rudder. I plan to use half of the boom, leaving ~8" from the ball center to U-shaped rubber support and horizontal clamp. (Yes, rubber support is desirable on my thin Kevlar deck). Like in this photo of somebody's kayak below. Torqeedo UL Facebook group is malfunctioning, my post has been pending approval for weeks. After company had been absorbed by Yamaha, there are delays with parts and motors, probably FB is a ripple effect.
https://i.postimg.cc/3wTj5Kzz/Boom.jpg