Thanks for the suggestion.
I got to looking at the guest_step tpl files that have code for a "Guest Checkout" title (which I commented out).
I compared the guest title code to the top lines of order_summary.tpl. It was pretty easy to emulate the guest code in order_tpl, and also a little educational.
I don't know php, but I'm starting to see some of the relationships & methods.
This is how I placed a small title above the sidewidt Order Summary, by editing order_tpl:
Delete line 3:
<h2 class="heading2">
<span><?php echo $heading_title; ?></span>
</h2>
Replace with:
<h4 class="heading4">
<span class="maintext"><?php echo $heading_title; ?></span>
</h4>
Thx.