Not necessary if you can't find them, mine is on normal ankle pegs and looks ok, long ones are good if you don't want a height decrease from the switch from ssc body to TT slim though - I was worried he would look too lanky and narrow with the extra height when I did mine.
If you use the red skull body with the TT narrow arms, I think the proportions of the (broader than normal tt slim arms) shoulders would even out the extra height though (sometimes it isnt about actual scale if it is about minute differences, but how you perceive the proportions as a whole lol)