That's why I said it's calculator time.
Try to find if the block has been decked. You might have to take it to a machinist to find out.
But you can still use published specs to figure out where you probably are.
Take a proper measure of
your piston deck height. Add the length of your chevy rods (center of pin to center of big end)
Subtract that number from block deck height. Result will be HALF of the stroke length you need.
OR: you can assume a 318 stroke, divide by two, and add rod length and piston deck height, and subtract that from block deck to find out how far down in the hole your pistons will be.
AGAIN, assuming you block hasn't been decked excessively.