Well - I think I have figured out the unit.
It does seem to be a 3 unit x 8 unit block.
If I use 6-3/8 x 17 inch finished unit, I can come up with cutting and assembly directions. (One unit = 2-1/8 inches)
Cut five strips 2 inches wide.
Sew them together with 1/4 inch seam.
Press.
Cut the strip at a 45 degree angle.
Make the cuts at 9-7/8 inch intervals .(I am reasonably sure the exact number is 9-3/4 inches, but it's easier to trim down a bit than to add a bit)
The triangles at the ends can be cut from 7-1/4 inch squares, but I would cut them 7-3/8 inches.
Sew a triangle at each end of the five-strip unit.
I apologize for the messy drawing - I just did not want to mess another piece of paper!