How do I display a block on an edit form for particular content types?
You need to add php code in the block Visibility settings in admin section of block. You can follow below code.

$node = menu_get_object();

   if (isset($node) &amp;&amp; $node-&gt;type == 'article' &amp;&amp; arg(2) == 'edit') {

     return TRUE;
   }

   return FALSE


Another example:

$nid = arg(1);

   $node = node_load($nid);

   if (isset($node) &amp;&amp; $node-&gt;type == 'article' &amp;&amp; arg(2) == 'edit') {

     return TRUE;
   }

   return FALSE