According to Edith Reiter's 2014 book, this instrument was completed on 3 February 1909 and sold to a customer in Portugal.
Howe & Hurd (2004) describe heckelphone #43 as a model 36b. As of 2020, it was part of the collection of the Museu Nacional da Música (National Music Museum) in Lisbon, Portugal.
The history of heckelphone #43 remains mostly unclear. It is likely that the instrument was acquired for the first performance of Salome at the Teatro Nacional de São Carlos in Lisbon, which took place in early 1909. Possibly, it belonged to the theatre until it was transferred into the collection of the museum.
A picture of heckelphone #43 can be found here.