Indeed - too much advance on the timing will shoot up the temps, so 1,2-1,5mm BTDC and make sure the contact gap at index is 0,38-0,40mm so you get full saturation on the exciter coil.
Stock head will work like a bad squish band on a overbore kit, best practice is to at least open up the union a little on a lathe (or even a drill press hack) to get a periphery that will angle the edge towards the center of the combustion chamber. Dont go too wild with the rework, but it can stand to drop a few points on the compression ratio anyhow at this stage.
...and Mobys tend to run hot to begin with, so keep that in mind as it will like to creep up to 400 easily. (edited)