why such precision? you are just looking for where the big pieces are going to take up space?..as long as the heads have room , the back of the engine isn,t touching the firewall,and the steering has room to go around the exahust you should be good with a real engine
On many of the builds I do that require a "mock up" motor the clearances are extremely tight. Sometimes the difference between building a header that works and doesn't touch anything is as close as an 1/8"[