They'll BOLT directly on, but the water passageways are different because the flow through the engine is different with the boss engines (not exactly sure how they differ, but that's what i've heard) i've also heard that you have to tap and plug a couple of water ports. Another problem with the boss heads is that you'll have to get an intake manifold especially for the boss heads because the ports are SO LARGE (i believe they're almost round). If you want to convert to a carbureted car it'd still be a PITA to get it to all work together but consider it impossible with a fuel injected car. Not only that but you wouldn't want heads that flow like those (imagine NO torque below 2500-3000rpm). That's an absolutely GREAT DEAL though. It might also be a good idea just to buy them in case you may want to use them in another project in the future or you could sell them for ALOT on Ebay. If i were you, i'd buy them, but not for the Saleen.
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previous name: 84stangLX
'84 Mustang 5.0 LX
my LX
'89 Mustang GT
my GT