What you are looking for is a 2551 "Zenel" Brake Wrench these are very rare, and bring big bucks from collectors. Here is what it looks like.
I haven't seen any reproductions in years. I can put you in touch with someone who will custom make you one, but that is expensive. The job can be tough to do without the tool, but if you can find a long 1/4 and 3/16 wrench it should do the job. I believe you could get a quality forged custom wrench made for about $200, a bit pricey, but that is what it takes sometimes. If you have any more questions I am here to help. Good luck, and Thanks for using Just Answer.I hope this helps, 100% satisfaction is my goal. If the answer is not clear, please reply and I will assist you more. When you're satisfied, click on accept. I don't get paid unless you do. A bonus and positive feedback are always appreciated, good luck and Thanks.