I went through all the floppy drives I have (the ones that are not inside of a pc right now). There are differences in length of the floppy drives I have but they are very minor. Longest is about 15.5cm and shortest is about 14.5cm.

I thought the LS120 3.5" might be shorter, but it looks like it's the same as a normal floppy in length (15cm).

Manual with dimensions of drive - http://stuff.is-a-geek.net/OnlineDocs/Hardwar … /ls-120_IDE.pdf

Pics of internals of LS120 - http://goughlui.com/2013/05/02/tech-flashback … s-120-showdown/

As it has to accommodate a 3.5" disk that's 9cm long there's probably not a lot of wasted space in those drives. Guess you'll have to look at either USB external floppy or maybe a 5.25"/3.5" combo drive if your 5.25" bays aren't blocked as well?

I have one spare drive I'll maybe try to cut the bottom left corner since this is unused space ^^
I want to put the drive in its 3,25 bay because it's integrated with the case (the case has the floppy drive button, left hole and slot)

As u can see there is not much space left but I still have the 5" bays 😀
Currently the left back side of the floppy hits the cpu

Newer floppy drives tended to be shorter.

If you can't get it to fit in a 3.5in drive bay, then you could just use a 3.5in to 5.25in adapter bracket so you can be done with this and get on with your build 😀
Another option could be to use a case that has more spare room at the front, depending on how well you are stocked on older compatible cases.

This is the problem with E-ATX cases. You carefully plan a build only to find that the parts you want won't fit in the case. Ugly kludges become necessary.

I had a similar problem with removable HDD enclosures in one of my systems.