You state "If I had flooded cells it would boil them to a crisp (or have to be regulated back)" - Here is a statement from Surrette Batteries that indicates otherwise:

"On a manual charging system the charging current at less than 75% charged can be 25% of the 20 hour rate. The rate can even be higher below 50% charged. Once the battery approaches 75% charged reduce to 10% of the 20 hour rate. At 85% reduce the rate to 3% of the 20 hour rate. At 100% the charge is discontinued. A well regulated fixed rate system will do this automatically."

If I do the math correctly - your 440AHr/24V system, (when converted to a 880AHr/12V system ), could, at the most conservative Surrette rate, be charged at 220 Amps until it's resting voltage was about 12.4V - that means your 280 amp alternator would be just about perfect for charging a set of eight (900 AHr) T-106 flooded lead acid batteries. Your 280 amp alternator, IF it were 100% efficient (how do you dissipate that heat?) would only charge the 880 AmpHour battery bank at 31.8% of capacity - still well within the Surrette guidelines for flooded lead acid batteries.

Again, I do not see the advantage of AGM.

After seven years using no maintenance GelCell batteries I now have eight years experience with plain old lead acid batteries. I have experienced nothing that would indicate an advantage for "Low Maintenance" batteries.

I am not trying to say there is anything wrong with AGM batteries - I just think the oft stated AGM advantages are overstated.