how to fasten wood joist to cinder block notch

I want to lay three 2×4 in the cinder block notch(as shown in the pic) as joist for synthetic deck, I need to fasten the wood to the cinder block in order to align the three 2×4 and to make sure it doesn’t move, I thought about filling the notch with new concrete and bonding agent but not sure if such a small notch of concrete will provide enough strength and durability. I might be able to put in an angled screw or nail into the wood and block, but not sure if that is the best option. Any advice is appreciated