Floor shifter vs steering shifter

[Swedchevy67]

When I bought my 69 I couldn’t inspect it myself,
since I live in Sweden.
The truck was original a steering shifter and not
a floor shifter truck as I noticed when I removed
the carpet.
I talk to the seller about it but he didn’t know why
it was changed.
Any ideas?
Now I like to update it to original, but I’m not sure
where to start and also not to finish.
Would appreciate if any one can give me a good
advice or send me some information on where to find
the right parts that I need.