Does it matter if I replace germanium transistors with silicon?
They were specified because it was 1967, and silicon diodes were still nascent technology. Germanium was first discovered and used for diodes and transistors, and were commercially abundant. Silicon transistors started replacing germanium but I guess not quick enough for that article. 

As mentioned, you want to use the PNP version like a 2n3907. And keep in mind that while they work in similar manners, germanium diodes have a forward voltage of 0.2~0.4 volts on average, while silicon will have 0.6 to 0.8 volts. So the transistors will not act in the same exact manner. 

This site shows 3 problems and solutions for converting a germanium circuit to use silicon. http://www.hawestv.com/transistorize/germanium1.htm for the most part, you will need to change multiple resistor values to get it to work.