Here are some links to tutorials on this board about 1/4" seams
http://www.quiltingboard.com/t-89997-1.htm
http://www.quiltingboard.com/t-109768-1.htm
other things to consider when blocks are not the correct size are pressing, not ironing, and using starch. I agree that you may not be happy with the results of too much block trimming on this quilt.