I'd just like to make a point about all of this before we go to much further. As has been highlighted above where this comment was made "Surely the factory must have had some form of approval for a race series cage, as I don't think the rules have changed that much over the years."
This is the main part of the problem, for over 10 years now WSCC has been telling the factory that their "RAC" bar does not comply with MSA Roll Bar specifications, yet it has taken then until a year or so ago to do something about it and bring out their "MSA" bar, although to be honest I have not checked if that is MSA Complient. So I hope you get the drift of where I lay a lot of the blame.
Now on to the serious stuff, anyone wanting to compete in a Westifeld in MSA approved Sprint or Hillclimb will need to have a Roll over bar that complies with MSA regulations. These have been quoted earlier on. Now I understand that no-one wants to spend money needlessly however I would point out that there have been occasions when Westfield's roll over so you can;t say it doesn't happen. The last that I am aware of was John Roberts Electric Westfield which was particularly nasty, the car was a very heavy car over 700kg. In this crash it significantly bent a Roll Over bar made to MSA specifications. So in my personal opinion I would be very concerned to compete in a car which doesn't have the right spec bar. Even more so when you consider that a lot of our competitors are as quick as many of the single seater race cars.
You do not have to fit a cage for any of our classes including Mod Prod, just an MSA complient bar, which are available from £ 260 upwards from a variety of suppliers, assuming you need to buy one.
There is no getting around it or any other fiddle. If you are not sure if your bar or cage is to the right standard then one way of checking is to get your local scrutineer to have a look for you, or ask at an event you go to this year.