Stock pulleys are 3.8" and make like 6-7PSI. 3.4's are good for 10-11PSI. They make a 2.55" pulley actually. I make about 5PSI on my 3.8" but my blower has high milage and I have good exhaust so its not crazy to loose 1-2PSI just making it flow better aparently.
I asked about that pulley Vs. header thing seeing so many cars with 3.4" pulleys and so few headers a few months ago on a GP board and 15 or so people said headers and nobody said pulley. The overall message was "only people that dont know what they are doing put pulleys on before headers."
It doesnt suprise me that a 3.4" would damage the motor if the previous owner ran 87 and stock exhaust. I see a bit of knock on a 3.8" and good exhaust on 89 so more boost, less flow and worse fuel would possibly cause it.











