Help with 413 Build please

Going from 413 bore to 426 is somewhat about .070 over I recall.
In short, a good way to ruin a good engine block.
By the way, what will the machineshop charge you for all this boring?

You might aswell get some proper sized custom forged pistons rightaway. Even more so because you want to stroke the motor, which makes you needing a custom piston in the first place.

Ofcourse there will be folks jumping in here and say you might aswell build a 440 for the same amount of money, but imo being different and able to say you have a 'built' 413 in your car is worth something aswell.