Today, dollar for dollar, is the 318 faster than the 340 ???

What part of a straight, untapered and still cross hatched good bore is stupid?
It had a small carbon ridge that cleaned up with a razorblade...

Why should an over bore help? ????

Remaining stupid I guess.
School me o'l wise one.
The original pistons have mated into that bore, new pistons are a hit or miss with maybe a tolerance difference. You will most certainly have to balance the assembly.