The Mach 1 internals are really no different that the stock Cobra rotating assembly. Forged steel crank (unless it was an Auto, in which case the crank is nodular iron), powdered cracked cap rods and hypereutectic pistons. The fact he replaced them tells me at some point the engine must have suffered catastrophic failure. Either that, or he knows the rods and pistons are the same and he's telling you it has Mach 1 internals to make you think the engine is even more special than it is. Either way, I'd listen to it run and have a compression test performed before commiting to anything.
I know you say you've made up your mind, but you're really making a mistake swapping out those 4.10's for 3.73's. The MPG difference is 2-3mpg at the most and the 4.6L DOHC really needs the added gear to make up for it's lack of bottom end torque and get the engine into it's power band that much quicker. A gear swap may not seem like much to you, but with these engines it could mean as much as 3-4 tenths in a quarter of a mile.....which is huge!!! The very least you should do is drive it around for a while with the 4.10's to see what you think of them before you go swapping them out. I’m not trying to get under your skin here, but you'd be foolish not to.
Thinking about the Mach internals, did he just swap a whole Mach1 block? That would suck loosing the Italian aluminium block for the cast iron version
The Mach 1 has an aluminum block as well, just not the more desirable Teksid unit like the earlier Cobra's. It uses the same unit found in the ’99 and ’01 Cobra (and possibly '02-'05 Explorer). Either way, the block will take pretty much anything you’re going to throw at it in a street car. Even the weakest modular blocks are said to be able to handle well over 600hp and I have yet to see one fail even at that power level.
he didnt get the chance to change the gears either so its still got the 4.10's for now
