yes, I was thinking I would probably have the mounting plate welded on the end and then have a hole in the side to post the motor in and allow it to be mounted up, just hoping there will be enough room to get the pullys on doing it like this.
I don't think it will be a good idea to weld a plate on the end.
How about making a motor mount with the appropriate centre hole and elongated slots made out of ali and make it wrap around the box on the outside left and bottom edge. That way the motor can be fitted to the mount and then slid into the box and bolted through the flanges of the mount into the steel box section.