Shoot for 10.5 - 11 range. (Assuming a gas calibrated wideband). Boost psi is irrelevant with these engines and the m90. Stop looking at it. Stop logging it. Disconnect the gauge. Doesn't matter. It will be different based on a thousand differnt factors including the weather.
Pick a reasonable pulley size. Set timing to 15* Check for REAL kr. If she knocks go up a pulley size or two. If it looks good change to 20* of timing. If it still doesn't knock drop a pulley size or two. Rinse and repeat until you find a pulley that's happy at 15* but KRs at 20* Set timing to 16*. Enjoy.
Ignore the people that claim timing > boost on these engines. In my experiance boost trumps all on these engines. I have played on the dyno and using the above tuning method I have seen less then a 2 horsepower difference between 15* and 20* once on the final pulley.
Once your done set your cruise timing to 43 degrees. Done.
