Is the frame designed to handle that source/location of torque?
A large portion of the uni-body strength is the battery. You would have to fabricate a full length frame in order to mount the running gear and engine/trans. It “can” be done, just not easily.
There are some builders of ICE-T (Internal Combustion Engine-Teslas) conversions on YouTube with links to communicate with the builders. By removing the ridiculously heavy battery pack, the frame might be thankful to lighten it's load, and based on the reduction in weight, the frame box might actually be overbuilt for the conversion.