Diameter of the balancer is not the issue.
And, although it's possible, failure of the flexible damper (the rubber coupling) is unlikely. It is bonded with strong adhesive at the factory to both the outer mass and inner hub.
If the bond between the three components of the balancer does fail, an index shift between the crankshaft and timing mark can occur. But (even though it's become conventional wisdom and is commonly blamed) it rarely happens.
More likely it's a parts specification problem. Often, a post-1976 balancer will be mounted on an engine with a pre-76 timing chain cover. The timing mark on a 76+ balancer is not compatible with the location of the timing tab on a pre-76 chain cover. In 1976 GM moved the slot on the balancer - CCW about 12 degrees.
Before the shift, when #1 cylinder fired and the distributor was properly timed, the balancer mark was at around 2 o'clock.
When post 76 SBC's are timed correctly, the balancer mark will be at about 12 o'clock when #1 fires.
Here are some images to help explain.
This shows a late model balancer on an engine with an early timing cover (what I'm guessing is your situation). The drawn-in arrow points to the hub keyway on one end and to where the timing mark would be on an early SBC. The actual mark is what you would find on a post 76 balancer:
A 1986 350 with stock balancer and timing cover/tab:
An aftermarket balancer with dual timing marks:
So anyway: if you want to time the engine using a timing light, you can either change the balancer or TC cover so that they are compatible. I'd just use the timing light and shoot the timing up around 12 o'clock (that's about 10 BTDC). It should be at least driveable if not quite factory spec at that point. Then, if you want, you can dial it in. Use the "hit ping under heavy load & retard a ****hair" method.
Note: the dates and degrees cited above may not be accurate.