Hmmm..
If we assume the previous owner's son stocked a maximum of 30 HBG in 07', and we follow the generally accepted theory that 90% of HBG are male, that would leave approx. 3 female HBG to overrun a 10 acre pond (with GSF nonetheless,) in the span of four years.

I will be the first to admit that, in the absence of a predator, HBG would do their best to occupy any and all available space. However, they are quite cannibalistic, and would consume some of their own offspring. In addition, more recent information would seem to suggest that F2's and F3's may obtain a nice size in their own right, not immediately retrograde. Something about the math doesn't work for me here.

I think there are some probable scenario's.

1) There were more than 30 HBG stocked.
2) They were GSF, not HBG.
3) There is another source of fish in this pond.

I only state this to make sure you realize what you're starting with, so you make the correct decisions for your goals.
Travism is right, HBG are not what you want for a balanced pond. How bad is the "overrun" situation? Could you post a pic of the GSF? Is there a creek, or other body of water feeding this pond?

You will probably want to establish your LMB first, in order to control your BG. Could you utilize the GSF as forage for them?

10 acres is a lot of pond to drain...

"Forget pounds and ounces, I'm figuring displacement!"

If we accept that: MBG(+)FGSF(=)HBG(F1)
And we surmise that: BG(>)HBG(F1) while GSF(<)HBG(F1)
Would it hold true that: HBG(F1)(+)AM500(x)q.d.(=)1.5lbGRWT?
PB answer: It depends.