Originally Posted by Trevtassie

If going steel, stainless would be the go no need to paint, but use a retaining compound to try and isolate the SS from the aluminium. A slightly thicker aluminium collar might cause less electrolysis.
Ream and face the headtube afterwards. Looking at where the crack is, it could be caused by the interference between the headset and tube being too small, it stretched the head tube causing a stress crack.