OE

Anyone out there remember their Old English rules better than I do?

I'm trying to make the smallest of adjustments to Caedmon's Hymn for part of the ocean in diluvium.

It currently reads:

Nu sculon herigean heofonrices Weard,
ece Drihten, or onstealde,
heofon to hrofe, [eth]a middangeard,
abieteende

Which in contemporary English would go something like

Now we must praise heaven-kingdom's Guard,
eternal Lord, the beginning established,
heaven as roof, then middle-earth,
breaking [with implication of storms]

I'm also thinking about replacing "or onstealde" with the bit from the line below, "He aerst sceop" (He first made), which is a bit better sensewise even as it discards the alliteration.

I got Cs and Bs in my OE and Beowulf courses due to trying to create good poetry instead of laser-accurate translations, but I don't want to totally botch this one. Any help is appreciated.