Yes, guess I misunderstood what you wanted. I thought you wanted two blocks together to measure 8 1/4".
To make an 8 1/4" four patch you would need 4 squares of fabric measuring 4 3/8" each.
You would need 4 squares measuring 4 3/4" each for a pinwheel.
You say your panel is 8 1/4". Are you going to sew it to the 4 patch/pinwheel? If you are not going to cut it or sew it, what are you going to do?