My research project is: «The complex analysis of the Āpastamba-dharmasūtra, Āpastamba-gr̥hyasūtra and the Mantrapāṭha as the part of the Āpastamba-kalpasūtra». It is a years-long research, which included Russian translation of the important parts of the Āpastamba-kalpasūtra: the Āpastamba-dharmasūtra and the Āpastamba-gr̥hyasūtra.
And I would like to attract attention of the specialists of Vedic Studies to the Mantrapāṭha. The critical edition of the Mantrapāṭha was published by Moriz Winternitz in 1897 (The Mantrapāṭha or Prayer Book of the Āpastambins. ed. together with the commentary of Haradatta and translated by M. Winternitz. Oxford, 1897). It supposed also to be the translation and Haradatta’s commentary in the second part of the edition but this part wasn’t published.
Hopefully, it may be possible to find this translation in the archive in Oxford where he had been till 1898 or in Prague where he had been since 1899. However, it is not mentioned by his students Wilhelm Gampert and Otto Stein, who made his bibliography.