Something like this should work for you.
Edit your form.php to:
<fieldset class="<?php echo $layout; ?>">
<?php
echo exhibit_builder_layout_form_item(1);
echo exhibit_builder_layout_form_text(1);
echo exhibit_builder_layout_form_text(2);
?>
</fieldset>
Then your layout.php should be something along the lines of:
<div class="text-image-left">
<div class="primary">
<?php if(exhibit_builder_use_exhibit_page_item(1)):?>
<div class="exhibit-item">
<?php echo exhibit_builder_exhibit_display_item(array('imageSize'=>'fullsize'), array('class'=>'permalink')); ?>
<?php echo exhibit_builder_exhibit_display_caption(1); ?>
</div>
<div class="exhibit-item-transcript">
<?php echo exhibit_builder_page_text(1); ?>
</div>
<div class="exhibit-item-description">
<?php echo exhibit_builder_page_text(2); ?>
</div>
<?php endif; ?>
</div>
<div class="secondary">
<div class="exhibit-text">
</div>
</div>
</div>
If you float .exhibit-item left and .exhibit-item-transcript right and then have .exhibit-item-description clear:both, you should get the effect you desire.