Geeezzz....that
is a pretty bike! The price seems OK to me and I'd give it a try with the stock exhaust for now.
On the modulators - the ones sold by Signal Dynamics are mainly for conventional (i.e. incandescent - halogen or not) lights. They may have a unit that will work on an LED light - but check carefully as the circuitry is different from one type of bulb to another.
If you want to run an LED - just search for a modulator that is suited to that type of bulb. I think I have an LED bulb in the taillight of my '76C (the effervescent Lucille
) and the
S-D Back-Off unit seems to work just fine there.
Another good replacement to keep these old girls perking is to use LEDs in the instrument lights. There are <I think> about 10 bulbs between the illumination, idiot lights and turn signal indicators in the dash - and they are all the same type of bulb. The place to get them is called
Super Bright LEDs
Pete