You can buy a 12 ball diff on speedmerchants website, that i think is cheaper than the IRS one, i am not 100% sure though. It is the diff that is included with the rev. 4.

KT hobbies has the team1rc tape that i have found to be the easiest to use and leaves no real resudie and holds in the batteries very well.

The speedmerchant tape has double the tensile strength, but its thinner so its harder to loop around and a plus and neg, it only sticks to itself, so if you need the tape to hold the battery in a certain position, then it wont work, but otherwise its really good and lasts forever (the roll is the same thickness as most other tapes, but since the tape is half the thickness its alot more tape!)