How to determine block module given block delta
No, it's not possible without having the module name.

Block deltas only need to be unique per module, so any two modules could implement a block with exactly the same delta, and you'd have no way to determine which was which without the module name.

The simplest proof of this in the code is the block_load() function, which has this signature:

function block_load($module, $delta) {


As you can see, even Drupal can't load the details of a block without knowing the module name unfortunately.