I agree, but I imagine they did what they had to do. It needed 2 batteries, 2 group 65's wouldn't fit, so they went with the largest that would. On the vans with the 1 battery frame mounted, a lot of van owners and mechanics don't know 2nd one is there. I had a COA van come in with a constant dead battery issue. Checking parasitic draw revealed the 10+ year old frame mounted battery and it's shorted cell.
Someone on here mounted 2 group 31 agm's on their frame, I forget who it was, but they had them mounted with the studs facing out for easy cable connecting and it looked pretty slick. The 2 problems I have with frame batteries is dirt/corrosion from being under the truck, and hoisting the heavy b@stards up there and then getting them connected.