Millions of cars drove for millions of miles without the front disc brakes. If the brakes are in good condition and properly adjusted you should have no problems. I would do a service check on them before you go. The biggest problem on the downhill's are a tendency to overuse the brakes and get them heated. This can lead to boiling brake fluid and blown out wheel cylinders and brake shoes. On the long down hills use a lower gear and do not keep your foot on the brake. You can apply them rather firmly and then lift off of them for a while. If they start to smell hot find a place to pull over and let them cool down.
Disc brakes are much better on the long hills because they have more stopping power on the front and also dissipate heat quicker than drums. With normal informed driving practices you should not need them but if you want to swap them out it is a better option. I run all drum brakes on my 56 Vicky.
Y's guys rule!
Looking for McCullouch VS57 brackets and parts. Also looking for 28 Chrysler series 72 parts. And early Hemi parts.
MoonShadow, 292 w/McCulloch, 28 Chrysler Roadster, 354 Hemi)
Manchester, New Hampshire