I and a buddy both had over heating problems using those blocks without the properly matched heads. You need the 452 with the tapered seats and holes to match the blocks. My truck and his Cuda would hit 230 plus easily. We were both using 906 heads. I gave up on my truck motor and put the 400 back in to sell it. He changed out his block with a 70 before it fixed it. I remember people having problems in motor homes after a rebuild if they used a head gaskets without the extra holes as well. Now I think all head gaskets have extra holes. We live in Texas and it is hotter than most parts of the country.

However, someone is going to say they ran the MH block and 906, etc heads and had no problems. Well, mopar designed it with holes in the block and holes in the heads to match for a reason. It was to cool the heads better.