Gradient inclusion - yay or nay ?

[Too Tall]

Hi all, As I am working on my layout, I had to tweak plans as I had Peco Streamline track spacing and even though I had minimum curves of 21 inches (Approx.set-track R3.5) at any point, it became obvious the clearance on corners may be an issue for longer coaches with large loco's like a Princess class.
My plans (on this forum) are to have a 2 height layout, but essentially 2 separate tracks.
While I was tweaking the curves for more distance beteween, I thought maybe I could have one of my upper level tracks have a bit of a dip as an aesthetic feature.

My questions are:

1: would essentially parallel tracks ever have been like this on UK railways (I presume they would flatten it so parallel tracks were the same height in reality) ?

2.the inclines would be around 1.4% and at the lowest point would be 1 inch below the adjacent track. Aas its a dual track trains would only run CCW on this track, so the decline would be mostly a 26.5" radius curve with a length of around 72", leading to around 62.5 inches of low level running fairly straight, then onto an incline the same length and gradient as the decline, but running up a slow S curve starting out as a 36" Radius, and opening out to 50 inches before leveling just before a bridge.

3: Can anyone anticipate this giving issues with running. This track will be running anything from 0-6-0 to 2-10-0 steam locos, running rakes of 4-6 coaches depending on loco, or similar length goods trains.

To paraphrase Yoda: Do,or do not? Your thoughts would be appreciated

[Walkingthedog]

There is a section of track on the Chiltern Line in Bucks where the lines separate. One goes out of sight of the other and at a different level. One section goes through a short tunnel the other doesn’t.

[Too Tall]

Thanks WTD, thats good to know

To help visualise, this is what I am thinking of doing. The light blue is standard height, the dark blue the section 1" lower, and the mid blue are the incline/decline:

[Mountain Goat]

In regards to your question about the prototype, Severn Tunnel is an ideal example where track goes down at different gradients at the eastern side which I assume is to assist trains on the upward gradient out from the tunnel.

[Walkingthedog]

You need a lot of room for a gradient. 1 in 30 is the recommended max so 30 inches to go up an inch.