Bob,
Sorry to hear about the diagnosis. I understand that there are some pretty good medications out there today for Parkinson's patients. I guess that's little consolation though.
I was diagnosed with Essential tremor a few years ago. It's kinda the opposite of Parkinsons, in that when my hands are at rest they do not have the tremors, but when I start putting pressure on the tendons (moving), the tremors begin. It really has reduced my ability to do fine soldering or anything that requires extremely fine dexterity. It started in the right hand but is also now in the left. Doc says no cure and not much that can be done except for beta blockers if it gets bad enuf. Anyway, I am still able to ride and hope to be able to do so for some time.
I wish you the best as you shift to a lighter handier bike. Keep riding and keep moving. Stay as positive as you can, thanking God for each day He gives us!
Regards,
Joe