Even if it seems difficult to understand,I have just found this old topic today and it's rather interesting,IMO.I can't speak about if cremation was an usual costume in the rural America of the 80's ,but about Spain,it has been more usual even than the bury in the last years,but not so much in this time.
However,I suppose that Jack had spoken about this possibility as he had signed already a will,as a way of letting everything arranged for his wife and,above all,his son.Yes,he was young enough as not to think about this still,but,as Tammy has said,his way of living-travelling a lot and,even,why not?,thinking in some unlucky "accident" during his Mexico trips...-might perfectly oblige him to have all these questions already decided.And it could be a good excuse for Lureen in order that nobody could see the signals of his violent death-specially,if it was not a mere traffic accident...-,what maybe was then the most important thing for her.I think they were living far from each other enough the last years as not to be interested in the way Jack had his last home,if it's could be moreover a "problem" for her social status.
As regards to Jack's wishes to be cremated,well,as a matter of fact this would be the only way of being free in the only place he had felt happy and he had been himself.For an only and last time in his life,the wind runs in his favour...