Funny, I was starting a 2 stroke chainsaw a couple of years ago. I yanked the cord, it kicked back, pulling my arm back down but the saw started up and ran anyway. But it would not cut at all. I killed it and restarted it and noticed the chain going the other (right) way and it was now cutting fine. It has started in reverse the first time!
So to accomplish this for propulsion, you'd add a reverse polarity switch for your starter and you're good to go.
You don’t want to do it very long, because they don’t make oil pressure in reverse.
US energy policy has entered the chat.
As you start getting into more complex engines, where you have fuel injection, timed spark plugs, oil pumps, transmissions it becomes untenable, but not because a v6 can't run backwards but because you'd have to rebuild and time all the support systems.
[1] https://chiefengineerlog.com/2022/06/24/main-engine-fixed-pi...
For example, a transmission would expect the engine to always run in the same direction, but given correct fuel and ignition timings, it doesn't really matter which way the crankshaft is turning while things are running.