Fully legal. At the time it was a MSA Multi-venue Autorest, many forward only auto tests held usually in farm yards etc. These changed name and turned into Targa Rallies. Great events for road going cars, which were limited to there appearance, they had to have full interior trim, were not allowed wheel arch extensions, nor roll cages etc. Engines must have standard induction systems etc.
Then just as I was getting the hang of the Jag LSD and grippy tyres they band anything more that 4 cylinders. A couple of us contacted the MSA but they kept saying "No".
Fun while it lasted and now I have a great fast road car, a true Grand Tourer.
mine used to sound like that too, but when getting historic club rego, the inspectors insisted that I have an extra silencer to make it quieter!
this I did and it lost its crackle that was so attractive, now sounds like any other modern car.....