I haven’t done an LS swap but those frame mounts look like the dreaded AutoZone “Performance Mounts”. (A2395) The clue is... They only have three mounting holes. One of them is in the center at the bottom. They bolt up to the frame like they are meant for the car. Try as much as you want.... They are different than the stock frame mounts and the engine side mounts won’t line up properly. You want part A2292 to replace the stock SBC frame side mounts They have FOUR mounting holes (in the corners) but you only use three of them. Ask me how I know. Thankfully, you installed them with the nuts on top which makes it a far simpler job to replace them. Good Luck!