In answer to your question, I am not sure about the master you are thinking about using. But I have two options for you.
First, I did see an original for sale on FleeBay the other day if you are interested. I think the seller is mikescp or something similar from Salem OR and the part may have been at his store. The problem is that this sort of parts accumulation is very pricey by the time you ship each little bit. Plus you have to bet that you can get it apart, rebuild it and make it work.
Another alternative is what I am doing. I'm putting a whole 550 front end on with tapered rollers in the steering head. The forks are 35mm and more sturdy. And I'm twinning the disks up front. I know it's not true to original but other than the twin disks and aftermarket headlight ears, it will be pretty close.
