This all started when I got a 55 Willys wagon. I learned right away that the master cylinder was near impossible to fill from the top and you can't see how much is in it when filling from the bottom without a mirror. I wanted to put a remote reservoir on to it to make it easier to fill. The choices I found were either billet aluminum or plastic and that looks completely out of place under the hood of a vintage car. I have built many hot rods professionally and run into the same problem of hard to access master cylinders under the floor. For the Willys I got an FC170 (Forward Control) master cylinder cap as these cab over trucks had a remote reservoir mounted to the dash. The first thing I saw was that the fitting was recessed into the cap and held lots of debris around the threads. I also needed a can for the reservoir and I found a place that sells cans with delta thread caps. Basically the type of can you get pvc glue in. I also found a vented cap that would screw on. In the end I had a rubber bellows in the top to separate the brake fluid from the atmosphere, a stainless barbed bulkhead fitting in the bottom of the can, and I sourced reproduction master cylinder caps that I modified to accept a 1/4" barbed fitting. After doing this for mine I thought that it would work on almost anything that had the master cylinder under the floor. I started to do some research into what master cylinder cap sizes there were. The Willys uses a 1-5/8" cap, Ford uses a 1-1/4" cap, Mopar and GM both use a very strange thread 3/4x18. GM also uses 1-1/4" caps on their trucks. So seeing a need I filled it, here are some pictures and contact info can be found in my signature below or you can PM me.