Question about bike modifications

by Jesse S. Samuel
(Chandigarh, India.)

I own a Royal Enfield 350 with a cast iron engine. I wonder if you've heard about this bike; it's a classic from the 1950s still in production in India.

There are a couple of things I wanna know about modification:

It has 3.00/90 19" front and 3.25/80 19" rear tires it has a 16T rear sprocket. Can I change the rear to a 110/80 18" or a 120/80 18" rear? If yes, will I need to change the rear sprocket as well? I've heard that to change to a 120, I need to get a braoder swingarm. Will these changes have any adverse affect on handling.

I understand that changing the wheel to a smaller size will alter the rake a bit. can I compensate that by raising the bike a bit by putting a spacer in the rear shocks (it has twin rear shocks on the sides)?

If I put an 18" rear wheel and raise the bike by an inch (which would raise it finally by ~0.5") would this subsequent decrease in rake have any adverse effect on handling?

What else can I do to alter the bike for better (not just speed performance but stability, fuel efficiency and longevity including).

Thanks and regards.