Well from the looks of Mike Boyd's hair cut, the racing jerseys, the fact Mike Boyd mentions he rides to hill 6 which has been in the closed section of glamis since 1991, and it looks like his bike might be a 88+ I'd say this article is circa 89-90. 

With a PT pipe there was/is no need for welded ears and case inserts b/c cases didn't cost $1,000 new, it was probably cheaper to just buy a new set.

As you can see times have changed and so has the HP numbers