You can still purchase a "std" 4.320" Bore ICON Forged Piston & std 5/64" inexpensive Rings....
Part #9953...which is a .070" over bore for your 426 (4.250" Std Bore)
https://www.summitracing.com/parts/uem-ic9953-std
Forged Pistons
$551.
E424K Moly Rings
$69.
This is your best and cheapest option
The ICON IC9953 is also very light,
and I would suggest Balancing is mandatory as you really have NO idea what target Bobweight was used in your 426 Crank ? and even if it is a 426 Crank for 100% positive ?