Welcome to the forum guys. Do you have any examples of the work you've done that you could post as pictures? I know there's a link to the website above, but it would be great to see some live examples here.
You just have to be careful with them as they can have a few major draw backs. The biggest one is a sticky throttle leading to excessive acceleration.
Once this happens its pretty difficult to fix as you'll pass 88 mph and end up back in 1955 where parts will be very hard to come by.
The second problem is your £40k buy price in 1955 money will then equate to just over £1M today. It'll be incredibly difficult to sell on at that point without making a major loss!