Don't worry too much about the weight of the brakes on a track, the biggest issue if they work well will be heat dissipation so they need to be big to put it in basic terms. I fitted a Wilwood conversion from D Jarman, used them twice and sold the car. The discs were so much meatier than the Pug ones I had and were a huge improvement. 15" wheels needed.
At first you will be fine though, I managed for years until me and the lads got quicker and hungry for laps.
Shell - just cut the rust out and make sure the anti-roll bar mounting areas are fine and the front 'beefed-up'.