Going 0 or Internal is not worth it on a stock rotating assembly, it will cost a fortune in Mallory/heavy metal to make that happen.
Your stock motor is 50oz, your balancer and flywheel have to match which they do stock. Since this appears to be a budget 306 just take the new pistons, wrist pins and rings along with 1 set of rod bearings to the machine shop, along with your crank, and 1 old rod/piston. Stock pins are pressed on to the pistons so you will need to have the old pins pressed out and then have the new pistons installed on the old rods. I would recondition the rods while they are out and add ARp rod bolts....any good machine shop can do this with no issues. Expect to pay around $150-175 for balancing, plus labor to press off the old pistons and install the new ones, have the block tanked, bored/honed, cam bearings and have the mains checked to see if you need an align hone. All said and done your looking at $600 plus.