Don´t worry, my PM was about the dihedral of the stabilizer. I read something about it but didn´t find the thread again. It said that the angle is less without the tuned pipe, or something like that.
Diego,
have you read Hanson's original MB article? He talks about the stab anhedral there based on the vertical frontal planform of the model (i.e., pipe or no pipe). If memory serves, for the 60, 3.5" anhedral with pipe and 2" without. Scale as appropriate for the 40.
The Pico was built using the 2" criterion being electric and having no exposed "exhaust" of any kind. Of course, the dimension is scaled for the 40" span. Regardless of whether you use muffler or pipe, I would build it per original 60 plan with the larger dihedral and anhedral, again, using the appropriate scaling.
I hope this helps,
David.