Hello Andy, The name I was after I think was Jim Balchin, The Comet can be made quicker, I did the standard road bike with Grey flash spec' engine, Open exhaust, Mk2 cam, Open up the inlet hole in the head, Bigger Carb' Maybe 9 to 1 piston, And was timed at 99.8 mph at the end of a Flying 1/4 mile. With your BSA gearbox it might be better to ride. As John said, I think you can do good things with altering the bore and or stroke, I plan a 560 cc Just on stroke if I ever get round to it!!, A bloke did very well in Vintage racing a few years ago, On a Matchless, I think with 84 bore and 102 stroke, I have the short conrod, Just need the flywheels altering, That way I can use standard push rods etc, I would prefer to use standard pistons, The BIG ones are a lot of money ?, and you would have to open up the Crank case mouth, But some people have done it ok. Good Luck, Bill.