I've added a anti-popping pull down resistor, a power filter cap, and polarity protection diode. There a host of modifications to the circuit you can find on forums and the like, but one I highly recommend is replacing the stock B1k fuzz pot with either a C1k or B2k pot. This will give a better sweep of the range of fuzz. It's also not a bad idea to replace the 8.2k resistor with a 10k trimmer or B10k pot (wired as a variable resistor) to help bias Q2 correctly.
There are many different transistors that sound good in this circuit (I've used 2N2222 and 2N2369 trannies with good success). Just use sockets and try different ones out.
I've verified the layout and put it in a 1590a using 2N5550 transistors. Here's pics of my build: