When going to a V8, there will be more stress on the driveshaft. If you plan to really launch your car hard, especially with a four-speed, we strongly recommend getting the sturdier V8 driveshaft; you can either have one made or locate one from a V8 car. Under normal transportation-only type driving, the smaller one would probably work fine, but who of us does that? Also keep in mind that Mopar offered two different size universal joints: the 7260 is the smaller unit, while the 7290 is larger and more durable; these need to be strong. Finally, if you are using an automatic with a fairly stock converter; this will be a little more forgiving since it's a "fluid coupling system" instead of a direct gear. The verdict: Better safe then sorry; upgrade to the stronger styles as soon as you can.