I would recommend Engelmann / Indian Rosewood. Myrtlewood doesn't sound anything like Rosewood -- it definitely falls in the Maple / Claro Walnut / Pearwood category -- meaning great articulation and less sustain. If you want a lush Cedar / Rosewood sound but with the clarity of a Spruce guitar -- then Engelmann will push you the farthest in that direction.
So my advice is to build an Engelmann / Indian Rosewood guitar. If you just want to build with Myrtlewood (which is a really nice wood to work with and is incredibly easy to bend) then also go with an Engelmann top. I built an Engelmann / Myrtlewood guitar and really enjoyed the tone.
Best of Luck. Also, you might check out the OLF (
www.luthiersforum.com) -- it is much better suited for an aspiring builder than the AGF.
Kind Regards,
Simon