I've managed to obtain some larger front brakes from a Riley 1.5 - they're pretty much a straight replacement for the original brakes, but much less prone to fading when driven hard. Considering I'm going to slightly improve the engine power, I thought it would be a good idea to improve the brakes too. The shoes and drums on the Riley brakes are enormous - they're wider even than those on the (much heavier) Land Rover, and I never managed to fade those. One slight drawback to them is that they have smaller cylinders than the standard brakes, which means you have to press the pedal harder to get the same amount of braking effort. I'm probably going to just fit them as-is and see how bad it is (I know somebody who's already done it and he says they're heavy but tolerable). If I have to I can always add a servo unit.
The other possibility is to fit Wolseley 1500 brakes instead. The shoes aren't quite as big as those on the Riley 1.5s, but they have bigger cylinders so they don't make the pedal heavier than the standard brakes. I've been looking for a set for months without any luck, and now the day after receiving a set of Rileys in the post I think I might have located a set of Wolseleys. They're described as being off a Riley 1.5, but now I have a set in front of me I can see they look quite different - I've fired off a query to somebody who has Wolseleys on his car asking if he can identify them for me. At least if I decided to go down this route instead, I got the Rileys for a good enough price that I'm sure I could just clean them up a bit and sell them on at a profit.