Beam question

I've replacing two load bearing interior walls with beams - my structural engineer has specified 300 X 100 beams to replace the walls - these are very heavy and a hassle to get up into the roof space.
My local timber suppiler has said why not get two 300 X 50 beams and bolt them together. Before I go back to the engineer, is this feasible to do this - any reason why these (bolted together) will not have have the same structural strength/load bearing as the 300 X 100 beams?

Thanks


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