am planing on installing one of the efi kits on my 1998 502 mag efi this week . was told by both manuf. to advance timing from 8deg to 10 deg , my question is if i already run 89 octane fuel do i need to go up in octane ?

I would, its cheaper than fixing an engine, although 2 degrees won't hurt anything either way. But if you did have detonation the knock sensor would retard the timing and defeat the whole purpose of advancing it in the first place.