I attached the jig to my table saw and the timber to the jig. As you can see I had to extend the bed of the router so attached a piece of ply to the bed.
The scarfs did not come out perfectly but close enough to be useable. The problem I did have was movement of the timbers while routing despite using some sacrificial timber and wedges to hold them in and down. The gunwhale timbers are now glued together and setting up.
Cheers Jay