the "match" for half-square triangles is easy. just add 7/8ths of an inch to the finished size of the square.
3" block finished.
cut the squares 3-7/8ths inch square
draw a diagonal line down the middle
put that square face down on a square of the contrasting fabric
draw another line 1/4" to the left, and a third line 1/4" to the right of the center diagonal line
sew on the left and right lines
cut them apart
voila!