but if a lot of work is done in iron heads or aluminium heads with some intake work and street friendly compression ratio it can be a killer little engine no ?
No. No way, no how. Can't run aluminum heads in F.A.S.T. either.
What exactly are you wanting to do here, build a 'street' motor or a F.A.S.T. type deal? Those cars are actually pretty well thought out and can be really expensive endeavors because of the class limitations. Takes a lot of creativity to make it look stock and go fast.
That said, if this is your entry into this form of racing, why make it hard on yourself? Forget the 318 and put a stroked small block in it. 440+ cubes will get you towards your goal way easier than trying to wring every last bit of HP out of an unproven and basically anemic combo. You'd be looking at a LOT of custom work to make the 318 happen - pistons, wildly ported heads and intake, rollerized trans, big converter... and in the end you'd still be working on a 318 2bbl.
There are a few stroked small block Dusters in F.A.S.T knocking on 10s which is incredible by any stretch.