Hi Bigdawgracer,
Yes you will need a low profile servo for use in the SRX4.
I bought one of the Xpert models, XP-PI-3402. Not the cheapest but certainly not the most expensive but has the best performance in terms of Torque and Speed for a low profile servo. (60degrees in 0.07@6v, and 15kg-cm @6.0v).
http://www.rccarshop.co.uk/index.php...-4-8-6-0v.html
Hope this helps?
Guy