First of all I have to say, depending on a used stock crank at 700hp is foolish.

Now how's it going to add up? 9.600 block, 3.58 stroke, 6.125 rods means the pistons have to be about 1.685 compression height. You said "Must be 1.123-1.125 length" which I don't understand. 4" bore pistons with a chevy pin size and 1.685 compression distance are not falling out of any trees. They're custom

a 350 chevy with 3.75 stroke and 6.000 rods needs a piston with compression height of 1.12, is that where that number came from?

Anyway, I agree with Cab that trimming the rods' big ends sounds like the right way to go.

The block can use every trick you can give it. Girdle, short fill, etc.

Good Luck!
R.