Analog Lab 4 as far as i can see is 64 bit only for both the standalone version and the plug-ins. At least the standalone version is by default installed in Windows 64 bit application folder.
Earlier versions of Analog Lab standalone versions was 32 bit and both 32 and 64 bit as plug-ins. All versions should be installed, unless you somehow do something to prevent this.
The main difference between using 32 and 64 bit applications is in this case how much RAM they can use. Beside that the functionality is the same.