This layout above would preserve the existing connection of the Great Western Main Line to the 'New North Main Line' through Greenford - but also upgrade the junction to be fully grade separated.
The Wembley lines would use the span under the North London Line bridge that was used by a now-closed freight line from Shepherd's Bush to Ealing via North Acton.
The up relief line from Greenford would be sunk into a trench, to pass under the Wembley tracks and it still be in a partial trench when it passed underneath the North London Line.
Looking east, this photo below shows the North London Line bridge from North Acton Central Line station (it is the grey/green bridge under the right-hand arch of the Victoria Road bridge. Beyond that is a minor pedestrian-only bridge.)
This photo below, taken further east from Victoria Road, shows a sketch of the Greenford Crossrail lines in the left foreground, and the Wembley Crossrail lines running off to the left.
|(1990 photo: Citytransport.info)|
Below is a video from 'citytransport.info':
"A quick spur-of-the-moment thing, when I decided to go on the once-daily Parliamentary Train service operated by a two-car 165 Chiltern Railways train, from London Paddington over the disused section of the former Great Western and Great Central Railway Joint Main Line which is roughly 11 miles long, stretching from Old Oak Common South Junction to South Ruislip (not in the video as my battery ran out at Northolt, What a Silly Billy) where it meets the Chiltern Main Line from Marylebone.
"This GWR section out to that junction is known as the New North Main Line." [HS2 will be tunnelled underneath it from Old Oak Common to the edge of London,]