I have those old Quilter's Newsletters, except one, with that pattern in them. I got them on Ebay.
Anyway, the churn dash block is in the 3rd installment. There is a diagram of the units for the block
and the caption says "7 1/8" Churn Dash Block Piecing". But I think 7 1/8" is the finished size.
The plain center square for the block is cut at 2 7/8". So all the little units have to measure 2 7/8" before
piecing together to make the block. When the block is pieced it should measure 7 5/8" before sewing
in the quilt.
Probably too much info, but hope this helps.
PS-I posted this info on your other query also.