what do you consider safe with n2o?
not blasting a 150 shot outta the hole in low rpms
your pistons would be ok, your rods may live too... you could possibly pick up 3-4 tenths...
i see plenty of lb7's and lly's running close to 650. pulling torque out of the tune helps rods greatly. Paint has been running close to 650 for a while right? IMO torque kills the rods not horsepower. and .3-.4 would get me into the 11's
but at what cost? you trying to compensate your lack of a lanuch by increasing stress on an already stressed and over-aired driveline.
a cost of 400 dollars
personally id just go back to the track and work on your 60's with your current set up.