Welcome aboard.
Fill us in on what state you're based in, as the rules regarding modifications vary from one to another.
For example, in NSW if you go over 200ci there are additional rules, so you might want to consider a 186 or 192. Any of these can be mated to the original crash-box, if you want to avoid big mods, at least at first.
You'll find stacks of information if you dig around in the forum here. Your local club is also a great source of assistance and advice. It's a hell of a lot cheaper to learn from other people's experience
cheers
RET