RE: .28 in a funfactor? oh dear....
Most stock 1/8 scale fly wheels are quite a bit bigger than the stock CEN one. If you get creative you might be able to re-use the stock CEN one. I know that a 3 shoe Ofna flywheel will fit the the stock motor on a JT chassis but I don't know how it will work with the big block especially if you had to space the motor up. I suppose that the main determining factor is how the flywheel lines up with the cut out in the chassis.
I haven't had a problem with my XTM sliding clutch in really dusty conditions but I haven't ran it in sand. I also haven't heard any complaints about them with sand. I suppose that the best thing to do is to e-mail one of the manufacturers and ask.
You are kind of on your own with the threaded insert, I have never seen on or heard of one in that size. Try checking with a local machine shop and see if they can make one. I the long run it might be easier and quicker to do this.
Exactly how much bigger is the Genisis clutch bell compared to an 1/8 scale clutch bell? I have never seen one so I don't know.
You might want to keep the battery and reciever were they are to help balance the truck. That is alot of weight that you added to one side of the truck.
rolland