Dave, 175lb is a pretty soft front spring for motorsport, but its all about the overall balance and there's more than one way to skin a cat. A higher roll centre will use a softer spring better too. Mine was pretty low.
I think the rear of my Datsun was about 180lb/in. It weighed in at 850kg with cage and 1/2 tank of fuel with about 450kg over the front axle. I've never tracked an A series 1200, but I would probably start at around 250lb in the front.
The 280-300lb figure for the cut-down Gemini coils was an estimate from the suspension specialist who does my wheel alignments. They had a few very quick Gemini series cars running out of their workshop so they should have a fair idea.