Hi machmike,
I just checked mine, and get the same BIOS version as you, "v4.51PG" - and I got a new BIOS chip from Gary Stone in mid-2018, so I can install larger harddrives in mine. It's got a sticker on it, that says something like "HDR BIOS" (didn't open the unit, but I remember talking to Gary about that).
So, I think you should have the large-drive BIOS, already (unless the regular and large-drive BIOS somehow shows the same version number?!?). I don't recall what the old chip said for the version on bootup.
I did remember where I put the chip that I pulled out, though, and it says this on the sticker - so, everything below is about the OLD chip (small drives) - just for comparison purposes:
AWARD ©1998
PCI/PNP 686
219850228
There's some more text that is covered up by the sticker, that looks something like this:
Winb...
W29C020...
008WI29527...
Interestingly, my OS showed version 1.3. I wasn't even aware I had an outdated version on it. I'll have to look into what 1.4 was improving/fixing, before I decide if I need to upgrade.
Anyway... from all I can tell, you should be good and up to date, with the chip/OS you have on your HDR
Cheers!