[XeTeX] fonts for units in math mode

[Faisal Moledina]

Hey all,

I would like the units in math mode to be displayed in non-italic  
font, but preferably using the same font that the math uses.  I'm  
using Lucida Bright or Palatino for my roman font outside of the math  
environments, and I haven't specified any math font (I like the  
default one).  However, I cannot enter units properly.  I searched  
around and finally stumbled on the SIunits package.  While that works  
well outside of the math environments, it converts the units to the  
Lucida Bright font inside the math environments.  It turns out that  
the fonts look quite different so this makes my units really stand  
out.  It's not any different from putting a \text or \textrm tag  
inside my math environment.  Even using the "textstyle" option with  
the SIunits package doesn't make it follow the math font.  Here is an  
example of my issue.  I tried a couple different ways with a couple  
variables, just to see the difference.  What is the proper way of  
doing this?

%%-- preamble
%mhchem package
\usepackage[version=3]{mhchem}

%SI units package :D
\usepackage[thinspace,thinqspace,textstyle]{SIunits}

%XeTeX fontspec
\usepackage{fontspec}
\defaultfontfeatures{Mapping=tex-text}
%\setromanfont[Scale=1]{Palatino}
\setromanfont[Scale=1]{Lucida Bright}


%%-- later in the document
To calculate the current that is attributed to \ce{Zn}, $I_{\ce{Zn}} 
$, equation~\eqref{eqn:ce} is used with the following constants:

\begin{align*}
n &= 2 \\
F &= 96485.31 \mathrm{\coulomb\per\mole} \\
F &= 96485.31 \coulomb\per\mole \\
M_{\ce{Zn}} &= \unit{65.37}{\gram\per\mole} \\
&= 65.37 g/mol
\end{align*}

It produces:
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Thanks to anyone who can help.

Faisal