Some general observations indicate that Sraffa has sided with Marx.
One can start with Sraffa’s edition of the works of David Ricardo. In that work, he collaborated with the Marxists Maurice Dobb. Ricardo’s work formed the basis of Marx critique of classical political economy. A point to note here is that Ricardo was concerned with the distribution aspect of political economy based on the labor theory of value.
In Sraffa’s 1960 famous book, equality of profits across industries are achieved by the free flow of capital across sectors, and not by the forces of the market as considered by Adam Smith. For Sraffa, relative prices are based on a theory of value and distribution based on social relation just as Marx’s theory proposed. Sraffa enhanced his model by using a standard commodity as an invariant measure of value, rather than relying on the market mechanism. Alfred Medio has shown that in industries producing standard commodities, the equality of prices and quantity implies equality profits and surplus value. Many post Keynesians hold similar views.
A final point: it appears that Sraffa was characterizing technology in term of what is socially necessary, a term that is characteristic of Marxian analysis.
Given the specific concrete purpose of Sraffa's contribution to economic science and the real effect of it, Sraffa could be considered not only a Marxist economist but a communist following scientific socialism as developed by Marx and Engesl in his own field (economics). Recovering classical political economy at Sraffa's time was one solid way to recover Marx's Critique of Political Economy in a field where Marxism and socialism are constantly repelled. There are now many unpublished notes from Sraffa that indicate his clear theoretical and political position in relation to class struggle.