Its called evolution...
Oh and quite possibly the rising price of copper
I ended up using the prestone flush, and spent a few hours first, making sure every single drop of old coolant was out before I added the flush into the system. Once I had run it for 20 minutes or so, the colour of what I drained out was as expected, brownish and a bit of grit throughout.
Refilled it and drove it again for 20 minutes, then drained it again and alot more crud came out, so just kept repeating until no more came out.
Then I ripped out my skinny NA radiator, changed the dreaded harmonic balancer to a new one with a new bolt for good measure, then swapped in my new fat TT radiator, and refilled with coolant.
Job done and hopefully no cooling issues in the future when I turn up the hair dryer