Did a quick test with Nebulus. Removed the first 128 bytes for each ROM. If you are on a Linux machine you can:
$ dd if=NEBULUS1.ROM of=nebup1.rom bs=128 skip=1
$ dd if=NEBULUS2.ROM of=nebup2.rom bs=128 skip=1
Then burned the trimmed ROMs on slots 1 and 2, invoked |nebu and it worked
Anyway I am wondering why is that header there and what is it for