Thanks very much for the help! I did have two of the resistors swapped. All the numbers are perfect now.
When I power it on, though, there's still a very loud buzzing in the background. As all the voltage measurements are within range now I'm really not sure what's going on.
Edit: I'm still experiencing this fairly loud buzzing in both channels; when the volume is turned all the way down, it's very soft, and when turned up the buzzing gets louder. All the LEDs glow and are in the correct position. The 2N222A transistors are both on the small boards and the 2N2907As are on the large board. The 237 ohm resistors are on the small boards and the 31.6 ohm resistors are on the large board. There are no solder bridges between the TIP-50 or MJE-350 transistors.
I've swapped out the tubes and the problem remains the same. All of the voltages are normal (A1 and A6 on the 9 pin socket read 76 instead of 90, but I assume that's close enough). Before installing the Speedball upgrade, the amp functioned perfectly. What should be my next step for troubleshooting this problem?