400 big block

I don't know what the HP/torque ratings were but they were not impressive. On to the other part of your question. The 400 blocks are a stout piece. The old way to hop them up was to stick a steel 440 crank in them and come up with a 451. With the proper pistons,cam and head work, you can get some real monster numbers this way and have a very strong block. I'm not sure that the cylinder walls are any thicker than a 440's but the webbing around the mains is much beefier making it a very strong block. I'm sure some of the more knowledgable guy's like BJR Racing and moper can fill you in on this setup.

Jack