Hey Grubby
My copy of British Civil Aircraft 1919-1959 Vol 1
Gives Auster 5 (1956-58 models) as
c/n
3401 GAOFJ 1st reg 9.1.1957
3402 GAPAH 31.4.57
3403 GAPBE 9.5.57
3404 GAPAF 14.5.57
3405 GAPBW 13.6.57
3407 GAPHU 13.9.57
3409 GAPNM 17.7.58
3410 GAPNN 17.7.58
All fitted with Lycoming 0-290-3/1 (pesco vacuum pump)
Dunno how many more there were.
TTFN