Wow, that's interesting for sure. How did the idle sound? I'm suspecting mine was street ported too, the seller didn't have much information on the engine rebuild, as it was done before he bought it. I'll have to contact the previous owner too!
Definitely believe it, with the modifications you've got, 350whp sounds do-able without a doubt, hell, even more with a street port! Not sure if you mentioned this, but were the turbos running parallel or sequentially?