please bear in mind that the tool needed to undo the head bolts is not a triple square, its a bi hex driver - it may sound the same (12 is 12 right)
the problem is the angles between the teeth on the tool.
This is also used to undo toyota cylinder heads - and people on the internet complain that toyota tighten it too much - so much so that their "triple square" tool breaks.
If you use a bi hex socket - it wont break . I bought mine from snap on - it was surprisingly cheap. - The snap on tool is short meaning you need to remove more stuff to access the bolt heads.
https://store.snapon.com/Double-Hex-Standard-mm-chrome-1-2-quot--Socket-Driver-Metric-Lexus-Toyota-10-Double-Hex-P646038.aspx
the difference between the tool head shapes is this
I believe the old 61x engines had the XZN bolts.