The steering block is the steering arm that holds the front wheel axles.. and the carrier is the "C" shaped hub that holds the steering arm.
steering block:
http://www.losipartshouse.com/servle...g-Block/Detail
carrier, or caster block:
http://www.losipartshouse.com/servle...C25-Deg/Detail
rear hub carrier
http://www.losipartshouse.com/servle...Carrier/Detail
You don't need to change out any of these parts... but some are using the GT2 front end parts because they are beefier...
Jammin CRT MM/Neu 1515 1700kv
Losi 8IGHT MM/Neu 1512 1900kv
Kyosho 777
T4 MM 5700
B4 LRP
XX4 MM 7700
old losi xxcr, MM4600 4s lipo 70mph+