It depends.
My -9 started life with an O-290d2. The O-235 and 290 share the same length engine mount (approximately 12" from the firewall to the back of the engine mount ring). However, I believe the the O-320 mount is 2" shorter, but check with Van's. The mount for my replacement O-360 is the same as the O-320's mount, which is approximately 10" from the firewall to the back of the engine mounting ring.. Scott, can you verify?
The other catch is the O-290 required a conical engine mount. I don't know if all O-235's are conical or not. O-320's came with three different style isolation dampeners.