I have 2 web services with about 6 web methods in total, most of the code is ofc sitting in assemblies any way, and the web service asmx is really just calling these assembly methods and returning their return type.
How much effort is it to convert the web services from ASMX to WCF?
I pretty much at this stage control the only - non web based clients connecting to the web services, so this is not really a problem, product is in prelaunch.
You should find it extremely simple to convert - especially if your existing asmx web methods are just calling into other classes. Just create a new WCF Service from Visual Studio - that way you still have your existing web services intact. It will automatically create an http end-point for your so you can just dump it straight into IIS (with a little configuration). You will need to describe your DataContract classes but that it trivially simple too.
I did this recently and it was a joy!