I like for the X-braces to intersect the lower corners of the bridge. That is the way most forward braced 1930's Martins were laid out. OM's were only produced until 1934, so all the originals are forward braced.
If you have an accurate OM pattern, you should move the braces (X, tone, finger) and bridgeplate up by 7/32" for the shorter scale. Soundhole and upper transverse brace locations are only moved up by 1/32". I always place the upper transverse brace 5/16" from the soundhole edge.
Measurements for the soundhole and bridge are from a 1931 OM-18 (25.4 scale) and a 1944 000-21 (24.9 scale).
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