Need to work with a list like it’s a string

It’s been a while since I’ve had to do something like this, and it’s just not jelling — I’m sure I’m making a basic, “it’s a list thing” mistake.

Here’s what I need to do:  take a free-text phrase that may contain spaces, force it toupper (not a problem), then truncate it to 12 characters.  For example,

Input:

Output:

Just can’t remember how to have Tcl consider xlateInVals as a string, not a list without getting an XPM Tcl Error.

Can anyone get me on the right track?  Or can this be elegantly done in a translate at all, or do I need to brute force it in a proc?

Thanks in advance!!!!