You can use the chips that you have and your existing Arduino configuration as ISP. The only issue with the '328 chips is that they have a different signature.
The trick is to change the signature in AVRdude so that it expects the sig of your chip:
Find your avrdude.conf file and in the entry under ATmega328, edit the line:
signature = 0x1e 0x95 0x0F;
to read:
signature = 0x1e 0x95 0x14;
Then do exactly what you did before and it should all work. Once you have the bootloader installed the chips behave in exactly the same way. I had this issue with a batch of cheap '328s I bought before I knew there was a difference.
Once you have burnt the bootlaoder, remember to change your config file back.