yeah I would agree with that too. if you are running the standard 160 hp, the TS box will be fine, no need to mess with the outputs. if you are going to be running 220+ hp, the TS box is probably too fragile. I cant remember what exactly is needed for the speedo. But if memory serves me correctly, the 83 type sender is analogue, where as the later stuff is pulse signal generated stuff, so you will need to change your speedo in the 83, and aquire a signal amplifier box and sender unit too. hence maybe easier as JJ says, to change the forward case?
out of interest, what re you looking to achieve going to the TS box?