I enjoyed reading your post
It sounds like you're on the right path for improving NA airflow. You might also want to consider a camshaft upgrade. IIRC the lift on the 1.6 cam is smaller than the 1.9's.. there's room for improvement.
I have a hard time believing the 150bhp 1.6 NA unless he ran nitrous. Giles' fuel inj. pump with LDA can provide more than enough fuel for 150bhp. It just needs a boost in air - either from a turbo or nitrous or whatever.
So if you want lots more power then have Giles add an LDA on your pump and do a few pump mods then hook up a nitrous system! But you'd also need a 1.9L TD headgasket and perhaps ARP or Raceware head studs.
Or just have a local shop install a LDA (cheaply salvaged from a broken TD pump) and use a small shot nitrous system. It may not make 150bhp but it'll be more reliable on the engine and the nitrous will last longer between fills.
Note: The nitrous sytem is to be plumbed to the LDA (in the same way it's plumbed to the intake manifold) so that the LDA will sense nitrous pressure and bam, more fuel while you hold the N20 solenoid switch.
The standard NA flow mods that you mentioned will still be nice to do.