Only difference between the x2-4977 and the D6 bios is the fact the D6 ignores the clock.
Sounds to me like what you actually had was clock issues, rather than issues with the x2_4977 bios itself, boot up the Xbox with new HDD in but Xbox has been unpowered long enough to reset the clock, so it ignores the DVD check and tries to load the dash straight away to set the clock (which of course, the dash isnt there, hence the error)
Best thing to do (provided you still have a working origional drive) is boot the Xbox from the origional drive first, make sure the clock is set (even set it again if you have to) then power down the Xbox and swap the drives over.
That should then allow the 4977 Bios to boot from the DVD drive and install the new HDD.
Of course, that will only work if you have a working origional HDD, if you dont, then what you say is fine.