Currently working with a buddy in my shop on his 65. We’d learned that he had the 6 cylinder motor frame stands which apparently are different than the 8 cylinder motor frame stands (apparently quite uncommon). Took several days fighting it, googling, and he even broke out Chargpt to figure out we needed to custom mount some SBC mounts in his car to get the motor sitting properly. But finally came out victorious and got the 5.3 sitting in there. Don’t mind the mess in there.