Gus:

You are most like correct about the fender mounts.....the Intruder has a wide front end and a narrow front tire - with a skinny fender on it.  The mounting points on the forks are extended to allow the fender/bracket to be small and light.

Trimming the mounts back shouldn't cause any problems - however you might have to drill and tap the bolt holes a bit deeper if they don't provide enough bolt hole depth when trimmed back.  You could also remove the mounts completely if you don't plan on having a front fender.

I run an 18" rear wheel and a 130/70-18 tire without any clearance problems with the swing arm.  If you get a tire much bigger in diameter than that and you may have a clearance problem with the cross piece at the front, and most people trim that back rather than lengthen the swing arm......as they can still use the stock rubber belt.  If you lengthen the swing arm you either need to convert to a chain.....or you could use a Kawasaki KZ750 rear pulley which has 65 teeth instead of 68 teeth and a longer swing arm to work with the stock belt.  If you are going with a 18x2.50 rim you should only be running a tire up to 120 wide - a larger tire will require a wider rim, and the 130/70-18 tire is supposed to be on a 18x3.50 rim.

The only way that I have seen anyone lengthen the stock swing arm is to extend the flat plates, RYCA sells pieces that are cut to fit onto the stock swingarm.  It would also be possible to get a second swing arm and splice the two together to make a longer arm.....but that is a bit risky as it will be putting more stress on the swingarm, and it was never really designed to be that long, and most most likely doesn't have a lot of extra strength built in.

He said 'twerking'