The first scarfer is a 7-1/4" inch worm drive mounted on some particle board.
To scarf cut the end of a sheet of plywood I put the plywood on saw horses and then clamp on a straight edge. And then move the saw tight to the straight edge.
A 7-1/4" blade barely cuts all the way through 3/8" inch plywood.

I need to scarf some smaller pieces of 1/2" plywood (roughly 16" inches by 24" inches) so I hacked an old 8-/14" inch worm drive so it can hold a ten inch blade.
To scarf those smaller pieces of plywood I fixed the saw flat on its side, and then move the plywood over the saw instead of the other way around.

7-1/4" inch blade



10" inch blade I cut the old blade guard off to make room for the big blade (hacked other stuff too) and then rebuilt the blade guard with plywood.

The easy way to scarf is to buy the West System attachment you bolt onto the bottom of almost any saw/

The homemade one attached to particle board is heavier. Vibrates less. Cuts smoother.

Yes, West Systems is ~ 90 minutes from my home. They still sell these tools.