This has been covered many times..
The 104 rear wheels have a deeper offset.
You need rear 103 tires to make it the same width.
Some have used the 104 offset tires and had good success with it.
We only run foams on carpet where I race so I can't help much there.
If you page back a bit there was a vendor listed selling rubber tires. Or have a look at the 103 103rm threads.