"Am I correct in feeling that a "Lee Speed" is only a genuine when it is stamped as such on the action under the bolt?
Some of the guns I looked at had very Lee Speed like finish and features but none were actually stamped "Lee Speed" anywhere."

Is a Mauser 98 a Mauser solely by name or is it more by design ?

To the purist ,I would say no it's not a Lee Speed unless it is so stated on the action .