If you mount the manual proportioning valve next to the master cylinder you only have to bend the 'original' line over to the new valve, and add a short line from the prop. valve to the rear line's port on the master cylinder. That's how I did it. I think I have a picture some place.

If you mount the valve next to the driver's seat, then of course you'll have to cut and flair.

I have a picture, but it isn't close enough to show enough detail.