Sorry for the trouble you are having. I am sure you will find a solution. I am surprised at the difference in the mounting you found. I wouldn't have expected that myself. Are you sure you ordered the correct part? Your linear drive
is either type 1 or type 2. Both have the same mounting mechanism. I have also seen linear drives that apparently are made for outboard
tillers the mounting mechanism is completely different. Most people who sell (resell) these don't have a clue and unsuspecting consumers such as us who buy them end up with, in fact the wrong part, and have to go through hoops to make a remedy.
Post a picture if you can and we could try and help. Someone will see the picture and may have come across the same situation.
Also, I have sent you a private message with a question. Regards.