I think mine is a 650cca and cranks fine even at 12v. Assuming you are talking about a 4BD1.
To be honest I'm surprised the 600cca didn't start it. Anyone else? Maybe the starter motor is getting on a bit...
Also supposedly you don't want to use a deep cycle as a crank battery.
(Edit: not sure if being an AGM makes a difference though)
Also, also, sounds like a buggered alternator?