Exchange 3-speed manual for 904

three speeds are the same length as a 904 automatic.

you need a ball and trunion automatic and it will directly swap over to the driveshaft.

In 63 your vehicle would have had a pushbutton panel for the automatic had it been ordered with an automatic to begin with. You can either locate and install the pushbutton set up from a 63 or 64 A body car OR use a 65 or 66 A body automatic steering column and linkage.

You may need a different carburetor....some of the ones made for a manually shifted cars did not have the arm necessary for your kick down linkage. Kickdown linkage is a MUST unless you tie the detent arm closed, failure to do so could cause the detent valve to open and you could kill the transmission.

All in all, not a hard swap if you can locate the parts. Finding either set up and getting it all to Sweden would be the hardest part, it's all bolt in from there.