KX100-great bike! I had a '99
You can lower the rear suspension by backing off the spring preload and/or running a softer spring. Also, the forks can be raised up in the tubes. The balance between these two affects handling/steering, so it may take a bit of adjusting to get it just right.
The 100 engine has way more low end, and is a much better overall or trail bike. Also, the larger wheels make it more stable than an 80 with smaller wheels. This is even a fun bike for a lighter weight adult (such as myself) to ride...the grin never left my face! I did some modifications to mine, but won't go into detail here...I assume you are looking at a 2002 model, so what I did to the '99 wouldn't necessarilly work on it.