Little difference from 55 to 58. But the Devil is in the details. Look. I mean look at the mounts. Will they bolt to the block? Some blocks were cast and drilled and some were not(in 55). The mounts will work? Good. The water pump...I don't think it was different..but I could be wrong..so look. Is the pulley about the same size? The shaft about the same (how long is it). Is the linkage for the carb in the same place? Those are the real issues. 55 has the same bellhousing so that should be OK. Will the intake/exhaust manifold go with the engine? Or stay with the vehicle? Some times the angle of the port was different, and sometimes the same. Unless you want a new pipe and muffler, I would leave the manifold in place and bolt it to the "new" engine. That is about it. If I am wrong..some one will let us both know. I hope.

Steve H