Steven,
yes, the 'viper' is basically the end bit as shown in those links you posted. Sorry for delay in posting - very busy so only getting the occasionaly evening to try to keep up on the posts.
Never used a laser line. I use a 1.8m spirit level lifted off the floor by a couple of bits of 4x2 timber. I then line it up across the edge of the tyre and check I have a similar clearance either side of the front wheel. once you have it set you just need to ensure you put the same number of turns on each side when you adjust the tension
