I have a X5 on Osmo. Now I have bought a used Inspire 1 with X3 camera. Will I be able to mount X5 on it. I believe that it may be Inspire 1 V1 not V2 with bigger motors. Do I also need any additional mounting plate for the mount.

Yes, it is possible. I know it works the other way. I have the I1 v1 with x5r and it works on the osmo perfectly!

There isn't much difference in the motors. However, you need an X5 / 5R mounting plate that is different from the default plate that comes with the X3. This is a USD 99 piece.

Mike hit the nail on the head.

In addition to the proper vibration board you will need risers for the landing gear , they  are inexpensive  and you will need them .  I would get the larger T48 batteries as well, dont expect super performance from this setup ( inspire  v1 with smaller motors )  but it will do the job .

donnie

DJI Vibration Absorbing Board for the X5 comes with the landing gear risers.