I have linked to this/my old post/information many times:
My 6v trucks use 2 gauge battery cables (and ground straps).
My 8+ year old Optima Red Top 6V Battery starts the 261 engine with no problems:
"1 Group Size, 800 CCA, 1000 CA, 100 Minute Reserve Capacity, High Power Delivery"
Sold by Amazon and many other suppliers (like Pep Boys). [and was sold by WalMart]
