Is 7C80 the ROM address?
That's not a RAM address.
I'm not sure which this Pointer Calculator program is, but it may either be not for NES or you're not using the data correctly.
The contents of ROM are not directly related to the contents of RAM.
If what you mean is the CPU ADDRESS, then on the NES you need to know the ROM mapping for the Mapper of the game you're using.
I believe Dragon Warrior (the English version) is using MMC1 (whereas the Japanese Dragon Quest was a CNROM game).
MMC1 is likely using a 16KB ROM bank size (MMC1 can use 16 or 32 KB bank size), so that means a ROM bank is $4000 bytes.
You subtract the header ($10 bytes) because that's not part of the ROM.
It leaves you with 7C70.
Now, you need to know what that offset is relative to its current ROM bank. Well, the ROM bank starts at $4000 (not counting the header, again) since that is the nearest lower multiple of $4000. So that means, it is at $3C70 within that bank.
The MMC1 can map two ROM banks in at once (with 16KB bank size), since the CPU allows 32KB of ROM to be mapped in at once.
I forget if MMC1 allows it to be changed if either bank is swappable, but most likely the bank at CPU $8000 is swappable and the bank at $C000 is fixed to the last PRG ROM bank.
So, assuming $8000 is the swappable bank, then your pointer is $8000 + $3C70 = $BC70. Or 70 BC, because NES uses a "little-endian" CPU which means addresses are stored with the lower byte first.
Hoping I didn't make any mistakes, as I had to re-read the message a few times to check I got the addresses you said correct.