I have been asked to share this information with one of the members of this site and am posting it here so others who may be interested in this can benefit. 

I made this jig several years ago (2006) while building a cedar strip canoe.  As I have begun to build my Drift Boat, I made changes to accomodate the different pieces the boat requires.  Also I have updated the clamps.  The drawing below has been updated to reflect the revisions.  The pictures shown below is of the current configuration.

The base can be made from MDF, Plywood or dimension lumber as long as it's flat & straight.  The riser for the locating edge and clamp mounting is made from Ash.  Any hardwood will do.

After the key is added and the riser secured in place, run the base across your saw to cut the right side dimension to match your saw's dimension.  Note: the fixture is designed to utilize the left key slot in the saw.  If you have a preference you can make your jig a mirror image to utilize the right key slot.

I added new clamps for the drift boat application, therefore the jig doesn't match the drawings.  I changed to the horizontal Toggle Clamps and added a new support for them.  With this configuration I have scarfed 1/4" x 7/8" Cedar Strips, the Inner & Outer Sheer Rails and the Chine Logs. 

By matching like grain patterns and the wood's color you can make the scarfs difficult to find unless you are specifically looking for them.

This is the bottom with the key aligned in the slot.  The base is MDF.  You can make the key longer, but the 8" long key I have used works fine, as most cuts are only 6-8 inches long.

The three pieces shown are:

1. The Cedar Strip is the piece to be cut for the scarf.  Align the end of the piece just past the vertical black line on the Jig.

2. The second piece is a scrap piece of wood, the cutting blade needs to break through the Strip and this piece allows that, so as to NOT cut into the Rubber Clamp Pads. 

3. The third piece is made to allow for the correct height so I don't have to adjust the Toggle Clamps for different applications.

4. Adjust the clamps to put sufficient pressure on the wood, so they will not move as you cut the piece.

5. On long pieces, you'll have to have a roller or other support so the piece remains horizontal and the Jig properly aligned on the Saw's Table Top.

The toggle Clamps are available from Woodcraft, Harbor Freight and many other hardware suppliers.

Hope this helps, PM me if you have any questions.

Happy New Year!

Dorf.