EDIT: I don't know if it's the paper you were referring to, but I did find this: http://groups.csail.mit.edu/pag/6.883/readings/p207-damas.pd...
I don't know if there's a free copy online anywhere.
The Damas-Milner paper is the sequel; it presents an alternate algorithm for type inference.
Benjamin Pierce's "Orange Book" is one of the best references now.
First link.
EDIT: I don't know if it's the paper you were referring to, but I did find this: http://groups.csail.mit.edu/pag/6.883/readings/p207-damas.pd...