Whatever converter came standard behind a 250 with a 350 turbo should work well. Don't get conned into installing some trick high stall speed converter at three times the price of a standard one. All that would do is create a false neutral at idle and make the tires chirp every time you try to take off from a stoplight.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!