What is this? Green box under dash wiring???

Not mine but may help you out.
Looks to be part of the starter interlock system.
I don’t have a 74 manual to look over the wiring so I can’t answer how hard to bypass.
NOS Mopar 1974 A,B, C, E body seat belt interlock control 3746653 | eBay


Found this on quick web search
Starter Interlock Delete? | 1971-1974 Dodge Charger.com