With respect Shaun, the M2 as represented by this kit was a full production model, not a pre-production/evaluation vehicle. I believe some 2300 M2/M3 vehicles were produced, though you are correct that most were upgraded/rebuilt into later variants. The actual prototype Bradley was noticeably different in appearance.
There are still plentiful photographs and publications available for references. - eg. http://www.primeportal.net/apc/epifanio_becerra/m2a0+/