My '81 Dodge van (bought from a gov't auction after a tough life) has the straight-six, and I'm guessing that my van weighs a bit more than your Dart, and I'm also guessing the van doesn't have much more (if any) power. While this vehicle will never set any speed records, it handles my Hobie-18 on galvanized trailer just fine, brakes are not problem in my case because it's a full truck. I did add a transmission cooler, something you might consider. DO pay attention to your brakes, but I'll guess you'll be ok if they are in good shape (hopefully they are at least disc up front) - don't cheap out on the parts there.