Jenkinsph,
Grading lawns is my main idea for a plane as well. Originally it was for new installs but now I'm thinking more about using it to topdress existing lawns. I roll yards in the spring and can shovel dirt into holes but a lot of times the whole yard needs dirt. Unless I rake it in or tear up the lawn there's no simple (low cost) way to fix some yards. Hence the landplane idea.
Thanks for the comparison info. Straight will be the way I go. I like your idea of making the blades adjustable. Better to have it and not need it than to not and need the adjustment.
Thanks again.
Lawnjocky