The stock T5 manual in the V6 is rated for 260lbft, and I believe the stock auto is slightly less, but similar. A 331 will make 300-350lbft. The stock tranny and rear will hold out "for a while". But that's about all that can be said. Exactly how long "a while" is depends on how hard you beat on it, and what condition it's in now.
Getting your stock auto tranny to work with a carbureted motor would be a real trick. Probably harder than most garage mechanics can accomplish. Remember that both the tranny and engine are controlled by a single computer, so if you want the auto tranny to work, you'll need the PCM to work even though it essentially 'sees' no engine. I'd wait till you have a manual tranny ready. Buy a junker T5 from a V6 if it's that urgent.
The cluster will present the same issues as the tranny (computer). MOST of the cluster (speedo, tach) could be made to work with some creative wiring of sensors and the existing PCM. It would be easier, though maybe not cheaper, to just replace it.
I'm going to be using GT-40Ps on my 351W. Best place to get stuff I find is to keep your eye on forums. Failing that, there's usually good stuff on ebay. I don't know of any online retailers that stand out in any way. If you're only looking for 270-280 at the wheels, unported GT-40s or probably even unported E7s will get you there with the right cam and induction.
