Frank
I was interested to read your post as I live on the TT Circuit between Dundonald and Newtownards. The last race unfortunately was in 1936 but you can find little sources of information around the circuit. The Old Mill at Dundonald has a small information area and the Start and Finish line in Dundonald is marked. In fact i will take my Morgan around the circuit regularly, pathetic lap times though, traffic lights and pedestrians get in the way.

A Bently roars by
The TT here is remembered, sadly, because of the dramatic final race, I believe by then crowds of 250,000 flocked around the circuit. On a wet day, a Riley driven by a local man Jack Chambers lost control in the wet. He crashed into the crowd near the Strangford Arms Hotel, some 1 mile from my home, killing 8 and injuring many others. I believe it then moved to Donnington Park a safer but less popular venue.
I have always been dissapointed that Morgan were not competing on this particular stage, maybe 3 wheelers not welcome. Also the first 4/4 was tantalisingly close to coming out of Malvern