Turbo 383 ?

I think you're yakkin'...lol.
You should be building a 400 block, not a 383. And, are you sure you dont mean a 318 from a diplomat? That will sort of attach where the Magnum in the Durango is. Twin turbo on an LA wont survive 15psi, much less 20+. The block cant take it. You need an R block to start with. NOS and a turbo? I'd suggest buying a complete package deal, including tuning and setup. Then you wont be yakkin', you'll be stylin' ;)