i would expect to feel significant eddy current drag from an alternator core, i think that's what you were using.
look for a motor typically used to drive the fan in a heat pump. if you're in the usa i could send you this one http://imgur.com/5iztOOb
after pulling just the stator stampings out of the sleeve. i have another motor of the same size so i could give you its stack and that would make about 3 inch deep core. i rewound the one in the photo btw just to see if it was reasonable for me to save the motor or melt the copper down. they pulled some shenannigans to fit an 8 pole motor in a 36 slot stamping, you might be able to tell the coil i fitted in there fits in 2 slots on one side and three on the other.
the motor in question is a 5kcp39kf but the ebay listings for that part number don't match what i have exactly. if you drop the last two letters off that part number you'll find a lot of other motors that are very similar.
anyhow the second problem is if your magnets are oversized you will saturate the core and the hysteresis and eddy current drag will be noticable. but if you're using the thick stator laminations from a car alternator, that may be half your problem.
you don't have near enough rpm to worry about what the magnets are made out of, or what's under them btw.
however if the core is saturated you may be able to measure the difference between pressing the stator core into an aluminum housing, or a mild steel one, or open air. some of those older motors had the stator stampings open to the outside air, primarily for cooling, so you may be able to more closely match the original look by bolting the end bells through the motor lamination stack with mere bolts, rather than a tubular shell that covers the entire assembly.
most car alternators did have exposed laminations, but the newer high output ones press fit the stator stack into the aluminum housing so that the aluminum can conduct the heat away from the stator!
if the stator is saturated due to the neodymium magnets you should get the least drag if the stator is not pressed into anything. a compromise would be a non magnetic stainless sleeve. it won't conduct the flux and its high resistance won't generate as much eddy current as most every other material will.