Your interpretation of the FARs is incorrect. To be compliant with
Part 103 the basic weight of an unpowered ultralight vehicle (FAA
wording not mine) must be less than 155lbs excluding safety equipment.
What is safety equipment? My interpretation is radio, transponder,
battery for such, ballistic parachute, necessary instruments for safe
flying (altimeter, air speed indicator, vario etc.) and oxygen and so
on. This brings the weight of my SparrowHawk up to about 195 lbs. This
actually makes sense when you think about it. You wouldn't want to
discourage the use of safety equipment. The other weight issue is the
max gross weight set by the manufacturer which includes the pilot
weight etc. With me flying the SparrowHawk I am below that limit.
As I posted previously the US FARs are out of date in many important
areas. If this subject interests you, check on the ultralight and
glider rules and regs in other countries around the world. What you
will find might surprise you.
Dave

You wrote:

I went to the Sparrowhawk web page where it
shows the empty weight as 155 lbs. Are you saying
that with a transponder, radio, batteries and oxygen
system installed the Sparrowhawk still weighs only
155 lbs?