Chris, I've been looking at the very same thing. From what I've seen I won't be using a factory one at any rate and mine is just a stroker 428PI. Of those that are available on ebay and elswhere the big difference seems to be RPM capability and SFI rating. Even though I'll probably never spin mine over 5.5k, I think I'll stick with the SFI part for piece of mind if nothing else. Who knows maybe I'll get froggy!
For the record, I'd love to hear some opinions of the builders that we have on this forum.
Steve