You would have no choice but to go with 7t if you run the 155 track. If your dealing with a stock 02 viper short track, it will have 9t drivers stock unless someone has swapped them out. The mtn viper didnt come out until 03.
Even if they were changed to 8t somewhere along the line, the 155 is a 2.86 pitch track and you will have to change drivers anyways. Thats the only way you will get it in there is with 7t 2.86p drivers. Along the same lines, that 151x2 is a 2.52 pitch and it will require 8t drivers to get it to fit.