The Ford Owners Manual on page 112 list the part number (BXT-65-750) for the battery. Specifically it is a Group 65 750 CCA battery.
For the house two deep-cycle Group 24 batteries were the original equipmentment per the sales brochure. Group 24 batteries are a bit on the low side regarding amp hour capacity. I would measure to see if two GC2 6VDC batteries will fit in the space provided.