I used 8779 brake boots that I purchase from Whitepost. They actually are a tight fit for those tiny front cylinders. They charged me a lot for those boots but it was worth it to me back then. Yours may be tight too but I haven't checked them. I know I had a heck of a time finding tight boots for those front cylinders years ago. I had Whitepost sleeve the cylinders with brass and had stainless steel pistons machined for my brakes. I used those tight boots and packed them with Red brake grease. At the time I found that the inner seals that Gordons sells were the best fit for those front cylinders. Before going through this I had brake issues every couple of years. Since that rebuild I haven't had brake trouble in over 10 years.
John Friese
67 White
67 Red