Are these threaded or do I simply heat the old block and twist them out?

 

 

Don, isn't that block to head?

 

yes block to head that the head stud / bolt passes through............they can be removed undamaged with a little "trick"..........

as for the block bell housing dowels then they are a solid "pin" with no thread so generally can be pulled........

 

oops clicked on the wrong picture link