Easiest upgrade from the 41mm calipers to those with 43mm pistons: Order them as refurbished/exchange parts.
At least here in germany you most likely (~80%) will get refurbished OEM calipers in exchange with the same marks/logos on them as if you would buy new ones from Mitsubishi, but at around 150EUR / piece.
New pistons + sealant kit is more expensive than these "new" calipers...
I got mine this way for 2 old calipers wich were only a rotten piece of rust.