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I've bought 3 85/86 engines, picking another up this week, but so far zero of them in a car. US 83 is plain 4.7, and 85 Euro is 4.7 S.
4.5 vs 4.7 vs 5.0, cubes are cubes, but main impact is the bore and limitations on the heads and valve sizes you can use. Euro S heads are shrouded, valve too close to the side of the cylinder for full flow, even with the 97.5mm bore of the 4.7L block. I don't think S heads are practical to use with a 4.5, and the Euro S heads are the MAIN cheap path to power. With 104mm a slightly larger valve might even be possible.
I would not be doing this if I wasn't pretty sure the incremental HP would not be more than incremental fun.
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