I think the following might work:
find:
Code:
<p class="calibre10"><span class="calibre12 bold">([0-9]{1,})</span></p>\s<p class="calibre2"><span=class="calibre4 bold">([A-Za-z]{1,})</span></p>
replace by:
Code:
<h1>\1<br />\2</h1>
There are more ways to do this of course.