I used AVO on my speedster with 300lb springs (should give you a starting point, I had a 915 so weight probably not too different)
I have just bought some Pro-tech coil-overs for my latest project and the quality is excellent, all aluminium for under £100 each. I will also be using them on my VWRX 1303 cabrio.
www.protechshocks.co.uk
You need to use 1.9" springs, last time I used 15" extended length, 10" closed which is close to stock damper lengths so you may want to alter that.
Hope that helps..
Rich