temple must definitely be more ancient than rr if it had a mangalasaasanam. but i remember seeing the asi's edict outside telling the visitors that the stone temple was built by rr( i could be mistaken)
i always wondered what a vaishnava temple was doing so far away from the rest.
start from kadal mallai( mamallapuram) go to thiruvidanthai. then move west cross the buckingam canal. reach singaperumal koil. take the route opposite , reach sriperumbudur orkanchi. so it was plum on the vaishnavaite route.