Type inference + overloading
I would suggest looking at Geoffrey Seward Smith's dissertation

As you probably already know, the way the common type inference algorithms work is that they traverse the syntax tree and for every subexpression they generate a type constraint. Then, they take this constraints, assume conjunction between them, and solve them (typically looking for a most general solution). 

When you also have overloading, when analyzing an overloaded operator you generate several type constraints, instead of one, and assume disjunction between them, if the overloading is bounded. Because you are essentially saying that the operator can have ``either this, or this, or that type." If it is unbounded, one needs to resort to universal quantification, just as with polymorphic types, but with additional constraints that constrain the actual overloading types. The paper I reference covers these topics in more depth.