Originally Posted by More_Cowbell
LOL, a 400 would be a monster if built right. 351m, no way, destroked 400... Same engine family as the 351C, but they do have their differences. The deck height is higher, the way I can tell them apart is that the 351m/400 are raised about 1" higher where the coolant neck is. The lower intakes are dry (coolant does not run thru them). But for the money and space, a Windsor would be the way to go. Cost to build a "M" engine is pretty steep.
For a '98, I would research and go w/ the ex engine. Down fall is the GT40-P heads with the different spark plug angles and using headers. But they are decent for stock. Heads are where the power is at, aftermarket heads would give a good bang for the buck. I have a spare 5.0L out in the garage on a stand with E6SE heads and GT40-P explorer manifolds, passenger side dumps up high and they are extremely restrictive. Thought about modifying them, but came to the conclusion that headers from scratch would be the way to go.