I ask why you wanted to remove the pipes. I reface heads with the pipe in situ by putting the pipe on the centre of a rotary table and fly cutting up to the edge of the pipe while the table is rotating. Scott heads are not top quality heat treated aluminium so do distort.
Latest gaskets seem to compress up more than the former copper asbestos type. I think I should revise my advice on head tightening to suggest that the end 3 nuts be a little less tight than the middle ones.
There is much less tightening capacity in the middle that at the outer ends so if we throw in a compressible gasket acting like a soft mattress then it is no surprise that it is possible to bend the head so the outer ends become deformed lower than the middle.
Just a few thoughts
Roger
