Hi Zybe,
Removing the nitrous plate should not be a problem, as the nitrous (and gasoline) is controlled by a solenoid. As a precaution, just close the valve on the nitrous bottle.
Below is the torque sequence for a 351C. Torque for the cast iron manifold is 21-25 ft-lbs for the 5/16" bolts, and 28-33 ft-lbs for the 3/8" bolts. If you have an aluminum intake manifold, check with the manufacturer for torque specs.
John
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