hey '90, I did just what you are talking about within the last 3 years. Bought a '78 2wd burby with a 454 for $300 bucks. It had about 140,000 miles. After pulling the bearing caps I realized I shouldn't have tore it apart. The bearings were like new. The cam was a different story though. To make a long story short, I had the BB and a SB machined and balanced at the same shop and built them myself. I've had both of them in a '79 burby 4x4. If you like torque, go with a BB, I liked the SB better in the dunes. The SB is still in the burby and the BB is on the floor waiting for the 400 SB in the K5 to die. As far as longevity, a four core radiator and an oil cooler will do wonders. It all boils down to what you would like to answer when someone asks what you are running for a motor. I'd rather answer big block any day.