Not a great deal,no .
one says "Tippmann 98" on the side
the other says " Tippamnn 98 Custom" instead.
The 98 has a sort of fish gill milling near the front which is is missing on the custom here's a side by side picture http://www.tippmann.com/markers/default.asp
the differences are on the inside.
The custom has spaces and access internally for Tippmann's drop-in upgrade kits which the 98 does not.