Weather it's the rods or the piston, or the crank.... The point is that it's the bottom end. On an expensive or nearly new motor, it might be worth it to drop the pan and repair it. Not on a 302W though, especially with some age and milege. Fix one thing and you'll be back in there sooner more than later.
COST, that is the question. It might cost more, but for what you get I say a 331/347 stroker shortblock would be best, but that would easily add up to about $3000+ once everything is done. A standard rebuild will cost between $1200-1600. How many miles on the motor. Under 100K miles and well taken care of you might want to see about having it refreshed. That would be possible if the cylinder bores and crank/rods are not out of spec, they can rehone and ridge reem the cylinders, pollish the crank and put new rings on and fix your problem for probally a lot less than even a rebuild.
I've got a fresh 306 never run in my garage, but it's a flat tappet motor, I would sell it cheap just to get rid of it. You would need the adapter lifters to run a roller cam in it.
