Hi Cymro,
49d - 5 letter "sign" (of the zodiac) + 3 letter "spread grass" (I only know this word from barred puzzles like the Listener) - initial definition is "wavered" as in oscillated but not a word I knew - thematic pair are first 2 letters.
You only show 9 letters but the original answer is 8 and then it's 10, but presuming your just missing one at the end, your A, which should be the 2nd thematic letter is wrong but the ?I?B?R?T?? are all correct.
Sorry if I've explained that badly but I've been up all night:-)