Before the 28lb the load was either 25lb for low level and 100lb for high.
Loads were either 8 of each or 16 of one. For T4 bombsight calibration it was 16x100.
At the time we never carried 21x1000 just for weight. There was a requirement for 2x1000 every 6 months but rarely achieved.
The only heavy weight load was the YS2 at 7000lb.
In Cyprus, to clear out timex stock we used to drop 7 or 14 1000 HE usually from a 2J popup.