It is hard to tell from the picture resolution any reminants of the origional diagonal Stop but I suspect the Guild Bigsby is an after factory add-on. For this guitar and Bigsby the string tension over the bridge may be insufficient to hold the strings in place. By the time Guild issued the M80 it had moved the location of the diagonal stop closer to the bridge of the M75 to hold the string in place. The M80 were issued with the closer bridge/stop location. I suspect that knowing this Guild would have installed a Bigsby with a tension bar similar to a SF5.
Hans, how do you read this configuration?
I must admit that a BLUE M80 is indeed an unusual color for the mid 1970's.
I would love to own that one.
M