exterior mirror help

[xRAY76]

this will be one of the first of many, many questions...

i have a 60 c-10 that does not have rear view mirrors, and i'm not sure it ever has.

i want to mount the 3 hole ''triangle'' mount style mirrors, and was wondering if there is some kind of template, or measurement to do so.

if my doors did have this style at one time, the previous owner did an excellent job of patching/filling the holes, i can't find a trace inside or out.

any pix/help is appreciated ...thanks