Manning Nash in his 1963 paper Burmese Buddhism in Everyday Life writes:
In a village household books are a rarity. If there is a book, it is a popularized version of the essentials of the religion given here, plus one or two of the better known thok [i.e, verses], like the heart and the diamond sutras.
Nash does not provide any further information about what is meant by Heart and Diamond sutra. But I have a hard time believing that this refers to the famous Mahayana sutras.
Does anyone know which texts here are referred to as Heart and Diamond sutra?
It’s probably the Heart and Diamond Sutra, of Mahayana fame.
It’s worth noting that the intellectual rift between the various buddhist branches doesn’t always trickle down to the lay people, who would admix various practices as they were exposed to them. Not just lay people, but monastics, as well. Fa Xian reports that Mahayana and non Mahayana monks and nuns coexisted side by side in the same monasteries; they just read different books.
Essentially, the stark dividing line between modern Theravada (which is, in essence, a reform school) and Mahayana was not always historically the case, especially not in some place like Burma, whose geographic lication left them open to lots of influences.
I don’t know a lot about the history of Buddhism in Myanmar, but Mahayana Buddhism did spread there, as well as Thailand and other Southeast Asian countries. There is even proof of tantra existing at one time in Southeast Asia. It was later that all of that was purged. So there might have been remnants of Mahayana hanging around here and there in the 60s.
As the article speaks of the texts being widely owned my guess would be that they are the Mettasutta and Ratanasutta. They can’t possibly be the Mahayana texts of these names as these are typically only known to Burmese scholar monks who’ve been to study in India.
That the author would misname the texts isn’t very surprising. Nash was an anthropologist, not a buddhologist, and reviewers of his books often remark to the effect that they appear to have been written in haste and their treatment of Buddhist matters is riddled with factual inaccuracies.
Regarding the remnants of the former Mahayana presence in Theravadin SE Asia, as far as texts are concerned these are pretty much confined to a handful of parittas and dhāraṇīs translated into Pali.
Hmm, yes, that sounds like a logical match.