If you look on the engine bay side, I think the engine is simply too wide at the firewall to allow a booster in the "normal" position. He could have used a linkage to have the booster over there and the brake pedal to the right of the column, but it would be complicated, and there may not have been room under the dash. Several Japanese subcompacts in the early 70's were converted to LHD (from home market RHD) with tubes running clear across the dash to the M/C on the righthand side. (the horrid Dodge Colts come to mind)

I don't know that there is anything actually illegal about the placement. I've seen handicap conversions done similarly (with a hand throttle). "Poor practice" for a street vehicle, for sure.