Quality of the aluminum casting as well as if the bolt hole and threads are cut to the proper size will determine if the thread inserts are a good idea, one of the brands of race heads we deal with we have to put in time-serts right off the bat otherwise they will pull the threads, customer and or engine builder are not happy campers. Proper bolt depth is crucial in having aluminum threads survive and as said before if you can put a stud in there instead of a bolt that would be my first choice.