Bit of a mock fit to get the distance from the chassis rails. The 50x50 will sit dead centre under the lip of the sill.

The drivers side is almost complete. Just need to support it at its final resting spot and tack.
The biggest issue at the moment is dragging my G size argoshield cylinder out onto the driveway so I can tack it because I haven't made a trolley for the new welder yet.