I picked up a 1977 three string McSpadden M8-W the other day. I had questions about the bridge and about the model number and contacted Jim Woods at The Dulcimer Shoppe for more information. The bridge was cut away under the bass string, and I had not seen very many M8's when I searched on the internet - mostly M12's. Here's what Jim provided regarding the bridge and the model numbers:
"The cut in the bridge was for compensation. The original string set is the same one we sell now as our Ionian set. The strings are all loop end type with the bass string being a wound .022 diameter and the others all .012 plain steel. The tuning would have been either key of C or key of D. For the key of C the bas string would have been tuned to C an octave lower than middle C and the other strings would have been tuned to G five steps higher than the bass. For the key of D they would have been one step higher than that (D bass and As for the others).
The first couple of years there was no real standardization of McSpadden models as they were sort of experimenting and developing their designs and models. When they did standardize, they offered the M8 and M9 hourglass models and T8 and T9 teardrops. The M8 and T8 were a little shallower and narrower than the M9 and T9. All of those were offered both as finished dulcimers and as kits for the customer to build. The design development didn’t stop and the deeper and wider M12 and T34 soon followed. (I don’t know why they chose to not call the teardrop version T12). Most customers preferred the larger models so they eventually phased out the 8s and 9s. I don’t have a date on that but it was late 70s. The current hourglass and teardrop models we make are basically the same size and shape as the M12 and T34. In 2005 we stopped using those designations and started simply calling them hourglass and teardrop."
My M8 is roughly 36" long, lower bout is 5 3/4", upper is 4 1/2", body is 1 3/8" tall, fretboard is 1" tall x 1 1/4" wide.
Picture of the bridge is attached for reference (not sure how to link to my gallery).