325hp 318 with 2bbl and manifolds is a pipe dream with a happy dyno.
An honest 400hp with a 318 would be on the radical side. lol it can be done, but it wouldn't be tame
Who said it has to be tame?
The heads they ported can support 400+hp, their gonna build cr one way or another, that leaves cam what they can carve from stock, exhaust manifolds aren't a huge restriction at low 300 hp, which leaves intake and carb the weakest link but is asking low 300 hp really asking a lot out of it ? Especially once their done modifying them.
If an engine builder with huge resources and willingness to put the time and effort can't build one hp per cubic inch I'd have to question his abilities as one.