Just wondered if anyone has any history on these things, I've found several links online to a place, Cole's Power Models that provides castings for some Wall engines, although not this one I don't think. Information seems thin on the 'net.
These plans are from a old magazine, Science and Mechanics craft print #177. This is a water cooled inline 4, 7/8" bore 3/4" stroke OHV. They were my granddads prints. I also have a copy of an old catalog/pamphlet listing all the different engines available from Mr. Wall at that time. These are roughly 50 years old or more, I could not find an exact date (don't have the magazine) but this was in a time before zipcodes as we know them today. :P
Walls Model Engine Laboratory
5900 N. Fairfield
Chicago 45, Illinois
The plans are fold out, 2 sheets roughly 24" x 36". Probably not the best design any more, but a neat peak into the history of model engineering perhaps.