If what you refer to as 2 piston, are the factory Kelsey-Hayes 4 piston calipers, rebuild kits and complete calipers are available at reasonable prices.
Moving to the LBP '73-'76 Abody front suspension/brakes involves not only replacing the front spindle and the associated suspension/brake components, it also means that you will need to replace your SBP wheels with LBP wheels. Unless you have these parts available including the wheels, the LBP change costs $$$, when you add up all the components.
Please search this forum for pricing and availability info. on the factory K-H 4 piston calipers and replacement rotors/parts.
