1966 Master Cylinder Question

[msw1968]

I have a 1966 Mustang with a 200 cid 6 cylander engine. The brakes work fine, except they dont have much resistence on the pedal. they are drum brakes and have the Screw on cap Master Cylander metal cannister. The screw on cap has a very large (1 inch) bulb on the underside that takes up most of the cylander space. There is no fluid in the cylander, but it doesnt have any fill lines so I do not know what if any fluid needs to go in the reservoir -- can any0one advise?

thanks,
Mike