I was recently in the same boat as you. What I did was find a quality machine shop. Disassemble my motor and took them the block, crank, rods & pistons. I also bought some Ross 82006 pistons and ARP rod bolts from Summit. I took those to the machine shop too.
They are doing all the machine work on the block and turning the crank. They are also prepping and installing the ARP rod bolts onto the stock rods as well as putting the new pistons on the rods. Then everything will be balanced together (flexplate, Romac balancer, crank and the rest of the rods & pistons).
I went this route because I was able to pick my piston of choice. Also, some of these "balanced" 306 kits are not balanced with your harmonic balancer and flywheel. Unless you current crank is cracked (be sure to have it checked well) I see no reason to buy an entire kit.
1989 LX 5.0 - AFR 165 heads, FTI cam, ported Edelbrock Performer, 70mm TB, Tweecer R/T, 306 w stock crank/rods and Ross pistons, MAC 1 5/8 long tubes, Lentech Strip Terminator Lockup and 3800 stall, 3.55 gears, Zex 125 shot
Running on E85