It's not a Class A amp, so heatsinks are not as critical. But the bigger the better. It depends on what voltage you're running at and what load you're driving (i.e. 4 ohms is worse).
I'm using something like the Wakefield 423K.
Thanks for the responses. In the assembly instructions Rod states that C1 can be anything from 1 mf to 10 mf. I have two caps in hand which fit the bill. One is a 4.7 mf electrolytic, the other a 1 mf metal film box cap.
Question: Is there anything to recommend one over the other or does it (as the instructions appear to suggest) really not matter as long as it is between 1 and 10 mf?
Well, the film cap would obviously be better. The cap, along with the input impedence determine the -3dB point. With 1uF and 22k it would be around 7Hz. If you need it lower, use more film caps in parallel.