Thats sounds like a great plan.
I would personally feel better if all the of batteries match exactly. But I see where you coming from.... More amp hours the better.
But what if they slightly charge and discharge differently? Perhaps over time you will have issues? I dont know but something to think about.
Post lots of pics of this mod.... Im very interested.
2017 Axis / 25.4: Big Foot Levelers, Aims 1200 Watt inverter, Ceramic Window Tint, Full River AGM 6V batteries, Front Hellwig Sway bar / Rear Track Arm, Safe T Plus Steering Stabilizer, PD 4655 converter, Hard Wired Surge Guard, WEboost + WiFi Ranger, LED Headlights/Driving lights, Fresh water surge tank, Black Tank Tornado flush, 4999 zip ties.