From the start of V8 production in 1955, all engines used the solid (stamped) steel clamp you show in the top picture. This was P/N 3704912.
Then, in late 1959 (for the 1960 model year), GM went "cheap" on us and used the wire clamp you show in the bottom picture. This was P/N 3772532 and used a "retainer" (P/N 3770598) to keep the legs from spreading.
Then, in early 1968, GM went BACK to the solid (stamped) steel clamp you show in the top picture (P/N 3704912). Apparently the wire clamp couldn't do the job, so in a rare move, GM went back to something that actually worked!
Now, as to which one you should have, it really depends on the build date of your engine. Very early 68 engines could still have the wire clamp. They were phased out, but still intermittantly used in early 1968 because of what they had left in inventory. Toward mid year production, the wire clamp had mostly dissapeared and the solid clamp was now prevalent.
Hope this helps.