There are products available that allow you to develop your own OPC server that don't require a lot of coding. If you know the protocol/physical media used to connect to the device perhaps you could develop one. Check the OPC foundation website.
Yokogawa has developed several Profiles for Kepware's UCON(User Configurable Driver) that the distribute for older devices that they do not wish to have a full driver written for.
if they have not done a profile you can get the Communications interface portion of the User Manual for the WT1600 and if it is a simple prortocol, whcih I suspect it is, you can create your own UCON Profile.