You really need to get yourself Karl Weissmann's splendid The Hawke History of MMM Competition Cars, available from the Library. In it you will see that G W (Geoff) McCrea drove 0259 and S A Durbridge (not Dunbridge) drove 0258 in the events you have listed.
Brian, Follow Simon's suggestion and purchase the "Hawke" book, available from the Register library it contains extensive histories of all 10 R Types.
RA 0258 at the date of your report was fitted with a Pomeroy/McEvoy twin cam cylinder head and by the time I purchased it in the 1960s it had acquired a two stage supercharger arrangement.
Confirm RA0259 is the Geoff McRae R-Type. In the official history of RA0259 there is considerable history of the car in the hands of Geoff (who incidentally helped my father track down the car in 1964). Geoff developed and drove this car to considerable success in probably all the hillclimbs and track events in Northern Ireland at the time. He collected a number of first outrights and even more class wins up to 1951 and competed in over 20 events, in a car that by that time was 16 years old and only 750cc. Incidentally Geoff was 10s faster than Dunbridge in the 1950 event mentioned.