Daniel,

See post #201 (top of page 9) with the "100%" 60 size plan that I scaled. If you read the post you will understand how to produce a scaled down version for any size engine or motor. For the 40 size original, simply scale the 60 by 0.9 (90%) and it will wind up having the 58.5" span desired.

As for the ribs, well, a little CAD work could help there.

David