Great project, love those bitube frames. Keep in mind that the fork was probably not designed for a low-rider rack both in terms of stability and geometry. Judging by the diameter of the fork blades and the age of the frame I'd be worried about the ride stability and the rake or lack thereof won't help either. I used a tubus tara and ortlieb sport rollers on my bottecchia traveller which has a similar fork and the front end was wobbling quite a lot to the point that riding free handed was effectively impossible. To counter this, I had to put my light stuff in the low riders which kind of defeats their purpose.