Reading along the bottom line, as I don't know if anyone understands the top line (corner) numbers, I think you're the twenty-eighth, California, twin bed, Land Yacht, Overlander of 1966
My references say:
SI246158(California, 1966 International Tradewind)
1st Position S (California) J (ohio)
2nd Position I (International Model) O (Overlander Model)
3rd & 4th Position Length
5th Position last digit of Model Year
6, 7, 8th Position Sequential Production Model. (Over 500 Double Bed, Under 500 Twin bed.
I think back then, the confusing, overlander "O" meant "Land Yacht" (non-International, base model). Any length could be an "O"
The "O" can be mistaken for zero, and the "I" can be mis-read as one.
The 5th position "S" ?? could be a mis-stamp, a special floor-plan or option?... I don't know, someone might...