Okay, at this point I figured it'd be a good idea to check my main source. Final /t/ and /d/ would indeed stay as [t] after a consonant, so that should be [avəˈlart] and [gaˈjãnt] (although that'd be the northern form, north of the Joret Line; the southern Old Norman form should be [dʒaˈjãnt]).
An important note, though: none of this is *really* based on Old Norman as such. There isn't or at least I haven't found any such detailed information on specifically Old Norman phonology on the internet for free. This is basically standard early Old French phonology (as per Frederick Bliss Luquiens's An Introduction to Old French Phonology and Morphology), on top of which the few known details of the Norman dialects are added (which is done basically by comparing standard eOF to later Norman and Anglo-Norman). It is only an approximation intended for Víkingr players, not for phonologists. I don't know nearly enough about eOF phonology to be more precise than this.
That makes sense, the discrepancies seemed few and more like errors on your part, no offense meant by that at all (God knows I make mistakes too). You're helping me a great deal here, since I'm providing extra names for the game Crusader Kings II and trying to give their pronunciations. I was having trouble finding Norman name pronunciations!