If master cylinder is blown and pedal is going down to the floor you wont know there are are hydraulic problems until the master cylinder is repaired. Normally, a line clamp test can be done to find a hyraulic failure, but with a blown master cylinder, the pedal will drop no matter what, so doing that test wont reveal anyother problems.
Yes, simply remove the rear drums to visually inspect worn brake shoes and drums and measure thickness of shoes to see if at min. specs, and measure diameter of drum to see if past max. specs.
The only thing you cant do is see if wheel cylinders are pushing the shoes out to contact the drums because you wont have any pressure to the wheel cylinders, so you wont know if wheel cylinders are functioning, but you will knwo if shoes and drums are good or not