[William Cloud Hicklin]

Tolkien was contemplating metatextualism before post-modernism was a thing. But he was never able really to carry it through (although there is a taste of it in the LR Prologue).

Personally I think it would have been very hard to pull off, even if he had been younger and more vigorous in the 1960s. Somehow he would have had to come up with some sort of really creative "garbling of the traditions" to suture over certain great big fat hairy problems, like Venus = a boat with a guy wearing bling,* and a very physical Frodo in an apparently material ship arriving in a seemingly concrete Eressea.

But he was certainly determined that Arda = Our Solar System and Ambar = Our World; in NoME he explicitly states, writing in 1960, that the Seventh Age was 1960 years old (i.e. = Aetate Domini)

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*The easy solution doesn't work- "Venus is just a hunk of gas-wrapped rock, and later garbled legend equated it with Earendil." The problem with that is that it rose for the first time as a brand new star within the living memory of certain persons still alive at the end of the Third Age, like Galadriel, Celeborn, Elrond and Cirdan, not to mention the Wizards.