Would this be equal in build quality as a Model M of the same year?
Yes.
But that's because it IS a "model M of the same year." You are asking if a Unicomp will have the same build quality as a Unicomp. You can deduce that they will (by definition).
The plate will be thinner than a model M of the late 1980's, the case is likely slightly different plastic. See all the articles meticulously cataloging the differences in the Model M keyboard throughout time.