If when you road test the bike you are happy with the performance then leave well alone. If not then do the job properly. Assuming that you have either MkI or Mk III cams then you can check for wear as the lift on both inlet and exhaust should be about 330 - 340 thou. Significantly less than this and the cams are worn. Then as to the timing. You do need to ascertain TDC properly, not just 'about'. Accuracy of one degree is quite reasonable. Then, at TDC, there should be more lift on the inlet than on the exhaust. The reason for this is that the 'degrees of inlet opening should be greater than the degrees of exhasut closing'. It says so in the book. Depending upon the cams and whether the followers are still flat or have worn concave you should have 10 - 20 thou more lift on the inlet than on the exhasut at TDC. The correct way to do all this is to remove the oil tank and front end and then use the DTI on the top of the valves and then take a reading all the way round each lift profile at 10 degrees of engine rotationi .e. 5 degrees of cam rotation. Check the base circles first by nipping up the tappets by about 20 thou and leave the tappets tight for doing the lift profiles. When you have the measurements plot them on a graph, a spread sheet makes it easy, and then draw a line at 5 thou lift. That is the figure at which Vincent valve timing is given. Work out what is the best compromise for your particular cam profiles as many Vincent cams are of really poor quality when it comes to the profiles. Your cam and follower hardening must have been right for them to have lasted so long. Pain in the posterior I know to have to do all this but if you are proper engineer the you know that you have to do things correctly otherwise your customers come back with the items you have made and threaten to use them as suppositories on you. Good luck.