[DKing]

There's some good books to take a look at on this. One is the Ford Parts Interchange, and another would be Steve Christ's "How to Rebuild you big block Ford". These would allow you to look up what you're being sold, to determine if you're getting what you think you're getting. Saved me once already on an Ebay 428 "Police Interceptor" engine. (It wasn't a "real" PI...)

In regard to Cobra engines, my plan is to go "cheap" and build a mildly wild 428. If it gets to feeling too weak, I'll build an alloy 427 later, when I have more dough to burn.

My reasoning for conveying this is that $200 for a 390 sounds like a good deal, based upon the prices for 428's I've been seeing --- providing that it doesn't have any cracks or repairs, and won't require an extraordinary amount of machining. You could pick up that motor (be it a standard 390 or otherwise) and build a respectable engine "on the cheap", and then switch to a monster FE later on. This gets your Cobra on the road for a smaller bottom line. Lot's of guys have 390's in their Cobras. From what I understand, even some of the originals had 390's, though most were 428 PI, 427 SO, and 427 CO.

Just a thought. Good luck!