There are many differences - 118 PY has concealed hinges, concealed petrol filler, swaged in side lamps, a slightly different roof height etc. Probably the dimensions are different - that's hard to confirm from a photo. 118 PY is 6 wheel equipped, 109 SK has the spare mounted on the rear boot etc. 118PY has weather deflectors above the windows and 109 SK has none.....
I have advertised world-wide for 136 PY, including all the places you suggest but it disappeared after the last known owner died in the 1980s. It will be sitting somewhere in a private collection.
Regards,
Brian