If memory does not fail me , it has been discussed before , but i cant seem to find the topic thou (might have been in another forum).
Anyway, what i recall is that the LRWW it not suitable for an efficient peltier block, because almost all of the cooling potential is centered on the DIE area , and respective fin's, and definitely not in the full area of a decent peltier. You'd probably would have problems cooling the entire peltier in a uniform manner.
You should try a Maze type block , or even a Swifty. Something with the largest cooling area for a given baseplate (and size of peltier). However, if you chill the water, and then use it in a cooling loop , then the LRWW is the block for you.
Well, i think so anyway.