You'd be better off asking this question at www.tccoa.com
(Thunderbird Cougar Club of America).
A '97 4.6 dohc was rated from 280 to 305 hp depending on application. The aluminum block is 75# lighter than the iron block. The '93-'98 aluminum blocks are known as Teksid blocks and can handle up to 1000hp without being modified.
From what I've read over at TCCOA, a dohc in a T-bird can be run with the T-bird's wiring and electronics. Everything bolts in, it's the same platform as the Mark VIII. It's actually a bolt-in swap.
If it's a Mark VIII dohc, $1500 is a little expensive. You should be able to find one for half that.