Thing is that a lot of the smaller Scottish clubs... as well as the Premier Division clubs at the bottom of the table like Motherwell, Hamilton, Kilmarnock etc... LIVE off of the Old Firm.
They rely on them to generate revenue for them. Example of that was the Scottish Cup draw. Smaller clubs PRAY for a game in the cup against the Old Firm because an away fixture to Ibrox or Celtic Park brings in a killing in gate reciepts. Even a home fixture brings in a ton of money as it puts bums on seats. I remember Airdrie played Celtic at home to a packed house just because it was Celtic.
Also the TV contracts for the SPL revolve mostly around the Old Firm.
So if you removed the Old Firm from the SPL, I'm pretty sure the whole Scottish league structure would just collapse due to lack of interest/funds and disappear into obscurity. Kind of like how I couldn't tell you anything about the Welsh league as the best Welsh teams (Cardiff, Wrexam and Swansea) play in England.
Plus the fact I was always under the impression that the Old Firm would be really good Championship sides as I think they would get slaughtered in the EPL. The style of football is totally different for starters. I just don't think they would be able to compete.
Be interesting to try this out in FM 09 though. I'll be downloading this db and trying it for myself. Hopefully the Old Firm can prove me wrong.