make a copy of your
calendar.php call it for example cal.php in the same directory of MyBB.
Copy the template in
Admin CP > Templates > Modify / Delete > Expand > Calendar templates > calendar
and create a new template call it
calendar2, we are still working in the template manager alright!!?.
in the copied template, remove
{$header} and
{$footer}
in the same code, just fix all links leading to calendar.php so that they become cal.php
example
<a href="calendar.php?year={$prevyear}&month={$prevmonth}">
should become
<a href="cal.php?year={$prevyear}&month={$prevmonth}">
Now open
cal.php
find
eval("\$calendar = \"".$templates->get("calendar")."\";");
replace with
eval("\$calendar = \"".$templates->get("calendar2")."\";");
now by accessing yoursite.com/cal.php