The key difference between the 4-bay and 8-bay panel antennas is the forward beam width. The 4-bay will receive signals from a wider arc than the 8-bay. The wide angle comes at the expense of some gain, which in your case is not a problem because you have good signal levels to work with.
If the existing antenna is not bent, broken or corroded, and if it look like this,
Log / Yagi then it could be used as a VHF antenna... just connect it to the VHF port on a UVSJ as TG suggested.
If you can avoid 'shooting' through the nearby tree(s) you'll usually see better signal quality.
I run a #10 or heavier copper wire from the mast to the nearest ground rod. I run the RG-6 down close tho the same ground rod where I install a coax ground block. The coax ground block is tied to the ground rod with a short length of #10 copper wire. I also verify the ground rod is tied to the electrical service ground system with a #6 or heavier copper wire.