The California missions are spaced approximately 30 miles apart, which was considered a days journey with the intention one could travel from mission to mission. This was, of course, with horses and wagons, etc... So about 10-15 miles a day back then is a reasonable assumption I think.

They seemed to manage moving the several ton blue stones from Wales to the site, a dead body seems trivial by comparison.

That's assuming the body was dead prior to arrival. For all we know they could have been part of the group delivering stones and died on arrival.

The scientists in the article suspect that the bodies were cremated elsewhere, and the ashes transported to Stonehenge.

Perhaps they would be more like roving barbarians.