One trim tab on the left elevator only.
Information I've seen on other forums indicates that this might be better stated as one functional trim tab only. I have seen pictures that I will post a link to that indicate the port and starboard elevators are interchangeable on the P-51. When built back up after its substantial overhaul, GG had trim tabs in both positions. The bellcrank on the starboard elevator tab is on the top surface, and on the port elevator tab, the bottom surface. The starboard trim tab may have still been ground adjustable even if that tab was fixed. For pictures of the GG rebuild, see
WarbirdAeroPress.com and
WarbirdAeroPress.com Wow, what an extensive rebuild!!