Hi Jawine
I'm not an expert on Ayrshire, but I have ridden the road on your second map and it wasn't very pleasant i.e. all main road which is a long laborious climb into the prevailing wind.
I have mapped out an alternative here
http://bikeroutetoaster.com/BRTWebUI/Course/662177which is a bit longer than your Dad's route but it includes a lot of minor / unclassified roads which go up and down rather than just upwards all of the time - and the total amount of climbing is about 30 ft less! It also passes the birthplace of Kirkpatrick McMillan (inventor of the pedal-driven bike) and Drumlanrig Castle where there is a cycling museum!
The only downside might be if you don't have GPS on hand you might get lost more easily.
Anyway, something for you to consider.
Jim
P.S. the GPSies site didn't show a lot of these backroads, so I couldn't map that route there.