Archings on these two instruments were very much like the companion mandolins, and plate thicknesses were essentially the same as for the mandolin. The H-1 had two transverse braces on the top, with the rear brace under the bridge. The Loar was tone-bar braced. The one slightly unusual point on the Loar mandola is that the peghead and the body scrolls were not scaled up with the rest of the instrument. They were basically the same size and shape as those details on the mandolin.

The book, The Mandolin Manual: The Art, Craft, and Science of the Mandolin and Mandola by John Troughton is available from Elderly Instruments (www.elderly.com/books/items/542-62.htm). Also, AL#51, Questions column gives some useful information and dimensions.

Several websites offer plans for flattop mandolas, though I have not actually seen them:
www.touchstonetonewoods.co.uk/ttwp2.html
secure.mimf.com/order.htm
www.art-robb.co.uk/plans.html

Jim Hoover of New Holland, PA adds:

The book Making Stringed Instruments — A Workshop Guide, by George Buchanan (Sterling Publishing) has a clean, scale drawing of a flat-top mandola as well as drawings of six other instruments, including violin, viola, cello, mandolin, and classical and archtop guitars with step-by-step do’s and don’ts.