I have an 11 year old MSD pro billet distributor on my hemi. The inside is crusty looking, but never had a problem w/ it. Recently switched to a crank trigger...runs the same. The rust evidently doesn't hurt anything.
For a crank trigger deal, you can run pretty much any distributor and be fine.

I have MSD 6al boxes on all our cars. I don't care for the MP boxes and the ridiculous claims made about the Rev-n-ator were enough to convince me never to buy one.