I've got a fan and clutch that was original (as far as I know) to a 67 440 GTX that I want to use om my 470. The clutch is not loose and turns properly but the aluminum part is grimy and the front face has surface discoloration (sort of rusty in color but there is no actual scaly rust) so I need to clean it. Short of degreasing and then media blasting, is there a better way to clean it (some sort of cleaner/solvent) that will not damage it and leave an original looking finish?

Soda blasting in a small blast cabinet works for me.

Hopefully it is not greasy from leaking. I cleaned mine up to only find out it was leaking at the shaft. Believe it or not I used spray starting fluid to clean most of it.

There's no way to bench test a fan clutch. Chances are a 50+ year old clutch isn't worth the time/effort you'll invest in it.

And will advise against any type of media blasting as the media / dust may penetrate the seals

Try Simple Green

I would also believe that a new clutch with new seals would be worth the cost.

To “bench test” a clutch rotate it with a drill press or lathe (devise a guard too)
and check the rpms of both inner and outer body with an adjustable strobescope that has an rpm readout.
Obviously the cost of the test equipment is high compared to a new clutch,
but adjustable LED strobes cost way less today in inflation adjusted numbers than the 1980s when they used Xenon incandescent bulbs.

i wonder how dawn "power wash" would work to clean the fan ?
you just spray it on, then rinse it off.
i have used it on lots of greasy parts, and it works pretty good.
however, i have not tried it on anything i was concerned about with a stenciled part number.