Engine Clanking LA 360 Motor

My engine makes a very loud clanking or pounding sound. It's more pronounced when you get your head near the oil pan which leads me to think it may be a thrown rod. The car idles fine and seems , it's a little sluggish when your easing into acceleration...sputters.

If the piston isn't moving up and down anymore, wouldn't there be black smoke coming from the exhaust since the cylinder is not compressing?

Anyway, does anybody have any idea the cost of repairing a connecting rod? If a new engine is in order, what is a reputable site for a 360 build and the cost of dropping it in. 1973 Dodge Dart Sport.

Update - Ran the car again today paying attention to the oil pressure guage.I only went up the street for about 5 minutes and the idle got really low and the pressure started dropping. Idle again was sporatic, something just isn't smooth about acceleration it sputters...

Thank you