That's a very cool mod. Thanks for sharing! And it sounds like it actually worked great too, which is always a plus.
I remember when the GC450 centerpulls were the ultimate touring brake. This is just before cantilevers made a comeback. After that centerpulls were seen as archaic and old fashioned for decades. (kind of like cantilevers had been up until that point)
FWIW I have one of those little ENE mini racks too. I got it basically for free in a package deal with some GC610 brakes. I decided the best use is to convert 80s mid level Japanese touring bikes into rando style bikes, and that it's sized for a small day handlebar bags like the Ostrich F-104N, perhaps specifically that bag. I was going to try to use it on my touring bike, but decided it isn't practical for camping. Maybe in this configuration it will work well for you though. I'd like to hear feedback.