I think that all Merlin engines from the Mk XX onwards until the 60 series used SU carbs that were fitted with “Miss Shilling’s Orifice” that fixed most of the negative G issues. Later 60 and most 100 series Merlins used a license built Bendix-Stromburg pressure carb (also called an injector carb, not to be confused with fuel injection, including early throttle body systems), with the original American item fitted to the Packard V-1650. The Merlin 130 series had a SU injector carb of British design that had little to do with the Bendix pressure carbs.

Nevertheless, the neg-G carb issues didn’t cause RR299’s accident, it was an issue of a mechanical failure that caused the fuel starvation/power loss.