They aren't. Size wise externally, as mentioned already, they are.
Some 318's will bore to std 340, but none would take the line bore to fit the larger 360 main journal and be worth a ****... you would instead grind down the mains on the 360 crank to fit the smaller saddle.
Even the 318 main cap is shorter and overall less beefier than a 340/360 cap.
You can do tricky things with experience... but watch out on blanket statements like that.