Like what Bullet said, being able to place coal or ground stackables would be a literal godsend. I can't tell you how annoying it is to keep up a cementation furnace manually! Is there any possibility of adding it as a feature using whatever function the "Crouch+Right Click" is based on for stackables?

It drops those on the ground BulletJustice.
(as if you pressed Q from the inventory)

How does this interact with placeables like Coal and Firewood? Does it slowly stack like it does from player, or does it drop those on the ground as if you press Q from inventory?

No it just places actually blocks into the world SalazarWindriver.

Will this try to place things like iron blooms onto an anvil?