Damsel in distress

Hi all... I'm the proud owner of Molly... My 64 Valiant. I've recently changed her ignition switch, bulbs, fuses, all the electrical wiring (thanks to being parked on a farm for most of her life), relay switch and got her a pretty hula girl... Along with of course oil and filter...

Took her on a outing and she was running like a champ until a loud bang in her engine and then she died and wouldn't start again... Popped hood and 1 spark cover was off and oil was gone (which I had just checked before I left).

Needless to say poor Molly sits in my driveway and won't turn over. Along with I changed everything except her old spark plugs because I'm retarded.
So...
Will getting her new plugs fix her?
Head gasket?
Need engine rebuilt?
Help!!!! Please and thank you