That's just it... the said someone just noticed (I have no idea why he didnt't realize this before) that the top has some 400-500mm straight section before it starts to taper.
This new topmast has a length of 365cm before it slides inside the 130/5mm bottom part.
Oh, how I wish I had a mental capacity of an organized engineer at least on some days to be able to keep away from these kind of stupid mistakes :/
EDIT: There is enough mast length to cut away the straight 60mm part. Does anyone have an idea on how to get the glued cap off, now that it's ok to destroy the part of the mast it's been glued to?