Dear All, 
Thanks Natalia for having asked about the 1955 brochure of the Vaajapeya Anu.s.thaana Samiti, Poona and on J.A.B. van Buitenen's 1955 film on the Vaajapeya and the accompanying typescript; 
and thanks Madhav and Michael and others for having provided authentic information on  these. 
Michael, you refer to a Pravargya performed in Delhi around a decade later, that would be around 1965. Perhaps there was at that time a big Soma ritual in Delhi, but I believe that the performance of large Vedic rituals was not yet that fashionable at that time. The urge to perform such rituals first in the areas where they were still marginally surviving or being regularly reinvented and adapted to the very new and rapidly evolving circumstances of the twentieth century -- mainly in Maharashtra (see now the recent sociological study by Borayin) and India's southern states -- and next to go with these 'treasuries' of symbolic value to the Raajadhaanii came a little later, one or two decades after Staal's recording of the 'last' great Vedic ritual in 1975 in Kerala, that is, in, at that time, strongly Kommunist Kerala (which was, in the Indian context, still a combination of communism and capitalism, the electricity company advertised itself extensively with slogans such as "power to the people" according to first-hand information provided to me by Henk Bodewitz, who assisted at that Vedic ritual: just to show that Vedic ritual, if it survives and wants to survive, adjusts to any political system that is in place). 
I am, however, aware of the performance of a Pravargya in the context of a Paundarika Ekadasha Ratra Soma ritual that took place not one but ca. four decades after the Vaajapeya in Poona, namely in 1996 in Delhi (yajamaana: Selukar Maharaj from Maharashtra). A few years later I produced a film on the basis of my footage with the help of professional ethnographic filmmakers Dirk Nijland and Nandini Bedi; this film I made available in the form of a VHS cassette that appeared in Leiden in 1999. 
At present two of in total three parts of this film have been made again available (third and last to follow soon) on my vimeo-channel on vedic ritual (vimeo.com/channels/vedicritual), which also contains other material on the study and performance of Vedic ritual -- incidentally, I received feedback from several colleagues who find these short documentary pieces useful in their introductory classes on Sanskrit and Vedic studies.  
With best regards to all, 
Jan Houben
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Jan E.M. Houben

Directeur d'Études, Professor of South Asian History and Philology

Sources et histoire de la tradition sanskrite

École Pratique des Hautes Études (EPHE, Paris Sciences et Lettres)

Sciences historiques et philologiques 

Groupe de recherches en études indiennes (EA 2120)

johannes.houben [at] ephe.psl.eu

https://ephe-sorbonne.academia.edu/JanEMHouben

https://www.classicalindia.info

LabEx Hastec OS 2021 -- L'Inde Classique augmentée: construction, transmission 

et transformations d'un savoir scientifique