Procedure help: stacking blocks like candles

I have Oysters in my MC mod, but with all the empty space, I want to make it so they can stack when clicked with another oyster-- like candles!

I already made the different models (two stacked oysters model, three stacked oysters model,  etc. etc.) and want it so the previous model disappears and is replaced with another. I tried this procedure and nothing happened! Can I get some help?