Automatic transmission oil pan modification

Hello, I have a custom made car with a house made chassis. I've been driving it successfully with a dog ring manual gearbox.

I now would like to switch to an automatic transmission. The smallest gearbox being able to handle 460Nm/340ftlb of torque that I could find would stick 3cm/1" under the flat floor of my car. I can't raise the transmission or the engine.

My question is: Is it possible to remove the factory oil filter located in the bottom of the oil pan, flatten the oil pan and then place an external oil filter system?

https://i.imgur.com/vDR6LrS.jpg

Why not modify the floor of your car?

Why not modify the floor of your car?
The floor would already have a hole for the transmission but it would still stick out by about 3cm/1".

I may have to design a skid plate to protect the oil pan from bottoming out. But that will only come if i do not find any solutions.

The gearbox I am currently looking at is the TCI 6 speed gearbox (http://www.tciauto.com/tc/6x-six-speed-transmission-package-optional-bellhousinghtml):

http://www.tciauto.com/media/catalog/product/cache/11/image/435x375/9df78eab33525d08d6e5fb8d27136e95/2/7/271601P2_6x_noBell_noShifter.jpg

I'll design my own bellhousing to fit that gearbox to my engine.