You have to use a boring bar to machine one housing bore at a time to their respective sizes. Since each main housing bore has a different size,you'll need to switch between 4 different sized OD rings to support the bar in each main saddle as you selectively begin to bore them. You might be confusing this with align honing the mains, which takes a long hone and hones the housing bores all at once, and to do that all the housing bores need to be the same size to accomplish this, and cant be performed on engines such as these.
