FYI, I emailed Carolinas RC and here is the difference between the SP2 kit and the SP1+SP2 bundle:

Hi Joe,

The SP1 with SP2 conversion kit does have the LSD diff in the front (as it
is just a SP1 kit with a SP2 conversion kit included). Other differences
are minor (shorter shock boots, lacks updated shock bladders). The good
news is that you end up with several extra parts after the conversion (SP1
chassis, hingepins, etc) that you can use as spares, or eBay. We only have
one kit left.

If you're interested in a pure SP2 kit, we will have them in stock on
Friday, and our price will be the lowest out there ($699)

Thanks,
Jon Martin
www.CarolinasRC.com