You remember Murphy’s Law? I decided a while back that Murphy owned a Tiger. My headers had been on the car for many years. I never thought I would have a problem re-installing them. It never occurred to me that changing heads would be that big of a deal so I never test fitted the headers before re-installing the engine. Wrong. I had bolt heads that wouldn’t get past surfaces they cleared easily the last time around. I finally bought some Allen head bolts to gain some space.
The jack under the engine method will work but if you have an engine hoist, you may want to use it instead. It lets you wiggle the engine side to side more safely. Those extra hands can then hold the engine to one side while you are trying to juggle motor mounts and header pipes on the other.