The limit hasn't been long been changed Welsho. I'm led to believe there was a fatality on that downward stretch recently on the road you mentioned, hence the lowering of speed limit.
As for specs when you're on the A77, the cameras start just after Kilmarnock and continue down to that roundabout you mentioned.
If you take the 1st exit which leads to Ayr instead of the 3rd which leads to Prestwick, there are no specs cameras until after the next roundabout (about 2 miles or so) when they restart again and run to at least the next roundabout (where you would go if you're heading for Ayr/Ayr racecourse/S&S etc).
i believe these cameras are all the way down the A77 to Stranraer, but i've not been down that road for many a year to confirm, only what i've heard.