If you are using the early style mounts,they should slip into the frame brackets. I've gone from big block to small block and back. The only time I had to move the brackets was going from 6 to 8. If you use the later mounts where the bracket bolts to the block,and the mount goes to the frame,just bolt the mounts to the brackets,drop it down in,center things up,mark your bolt holes,remove engine ,drill holes and re assemble. Hank