A stock World Class T-5 isn't even close to strong enough behind 4-500HP - ask me how I know (crunch, crunch, crunch...). If you want a 5-speed, spend a few bucks on a G-force T-5 or Astro Performance A-5; both are basically upgraded gear sets in stock T-5 cases. Toploader 4-speeds are virtually indestructible if you don't mind not having an O/D gear. If you want to use a stock T-5, make sure you have a towing plan on your insurance, and be prepared to get really good at swapping transmissions in and out...