my observation on electronic musical "things" is that the designs tend not to be "careful" about minimizing the effects of semiconductor differences. (In a normal audio amplifier, one does things to ensure that the actual gain of the amp is not dependent on the exact gain of the transistors being used, for example.) That means that you can probably get SOME interesting behavior with a wide range of similar transistors, but if you want your box to sound exactly like "the original Xyz TB-ABC effects pedal", you may be stuck hunting to the exact components specified. (witness the scramble for rare parts for Adafruit's x0xb0x kit, for example...)
Otherwise, Grumpy's advice sounds spot-on, as usual.