Absolute sudden-stop-no-spark points to a wiring problem. Fuel problems give you some kinda warning.. Wiring problems happen all of a sudden.
My first guess is a wire connection . Since you guys went deep into the engine you musta moved a lot of wires around.. triple check all connections especially the ones you cant see.. like tug on everything to make sure it's really connected.
Another thing is some wire might be misrouted and got burnt and grounded or got pinched and finally broke or grounded.
I dont suspect a mechanical or electronics problem.. it's a wire.