It turns out that JRRT actually translated several of his early works into Old English. His plot device was to be an Anglo-Saxon mariner who accidentally found his way to Tol Eressea, "the Lonely Isle," and learned the legends of the First Age from a survivor of the wars of Beleriand, one Pengolod (or Pengoloð)
So, for the sake of verissimilitude, Tolkien wrote, among other things, an early draft of The Annals of Valinor completely in OE. Compare
M Her, æfter þam þe Valinor wearð getimbrod, 7 Valmar þæt is Godaburg, gescopon 7 onwehton þa Valar þa Twegen Beamas, oþerne of seolfre oþerne of golde geworhtne, þe hira leoma onleohte Valinor. Ac Morgoþ bude on middangearde and geworhte him þær micel fæsten on norþdælum; and on þære tide forbræc he and forsceop hi micle eorðan 7 land.
In the Valian Year 1000, after the building of Valinor, and Valmar the city of the Gods, the Valar brought into being the Two Trees of Silver and of Gold, whose bloom gave light unto Valinor.
But all this while Morgoth had dwelt in the Middle-earth and made him a great fortress in the North of the World; and he broke and twisted the Earth much in that time.
N.B. The OE sign "7" is like our ampersand and substitutes for and, ond in many OE mss.