Calculating resistance with a multimeter
I did a search for Guitar Research T64RS and found a reference to it here: http://music-electronics-forum.com/t38041/. The poster was asking about the type of mains transformer, but he had very conveniently attached a good enough photo of the circuit board. It should be easy to determine if this is the same board as yours. If you zoom in you can see R67 about halfway down the photo. To me it appears to have the color code BROWN-BROWN-BROWN-GOLD which is 110 Ohms 5%.