C110 copper is the way to go, unless you have a cheaper source for something else. Silver will yield a very small improvement which you might be able to measure.
Your fins are too tall, at 7mm. Cathar originally went with 5mm, based on his thermal simulation, and eventually dropped it to 4mm.
Your nozzling plate needs to have a smoother transition. Your current configuration amounts to the equivalent of a couple of orifice plates, which is more restrictive than an actual nozzle.
Cathar went with a baseplate of "less than 1.0 mm", if it's any help.
Are you planning on molding this block together, or machining it into shape?
Here's a tip (useful as a guide) on the nozzle:
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