Hello,
Well you would have to think that there would not be an upward limit as to type of setup you could install 4.6 on. Most if not all the products only say that you need at least one setup or another, never to not use better software or hardware. You would be better to check out any issues with the Java environment an what running 1.3.1 means compatibility-wise.
I too would recommend that at some point you upgrade/migrate your environment to utilize one of the two most recent releases (6.1 or 6.5 in this case), just so you have continued support for running productions and future developments.
#webMethods#Integration-Server-and-ESB#webMethods-General