Is 79 on a practice ASVAB a good score, for EOD? For Combat Engineer?

You would definitely be good to go as a combat engineer and I would guess that you would be qualified to be EOD. It will all depend on your line scores from your actual ASVAB. Just take a few practice tests and you shouldn't have any problem (case in point: I got a 75 on the little 20 min one they gave me at the recruiters office then did a little studying and got a 95 on the real one)