That serial number is in my database, so I have seen that one before. I have i listed as a 340 SS from a Mike Vasser (is that you?)
So in 1978 there were not separate SuperStock and Super Mod models. There was The Superstock and then the factory race sleds, which are very close to the SS's.
In 1977, ALL the 340s started out with the individual cylinder motor, half way through the season they migrated to the monobloc because it has more torque coming out of the corner.
In 1978, all the 340s were monoblock. The factory had the larger pipes AJ speaks of, and as the year went on, they gave those pipes to a some of the independents (TJ Patrick, Team Frustration, etc) The 1979 upgrade kit came with the larger pipes.
Your handlebars, front suspension, and everything else indicates this started and finished life as a Super stock. It is in GREAT shape.