there are many vette style mc and caps. post a pic of the type of mc you have if you have a specific need.
most caps cannot be converted as they don't seal well and are vented, you would need to make one.
make sure any parts you use are brake fluid tolerant, no rubber or rtv
the link sedanbob posted would be easy to make with a chunk of aluminum, a brass fitting and a reservoir.
i was able to convert my ford mc into a remote reservoir using junk yard parts and teflon hose.