The 430's are a better shock.
My original plan was to get some HD springs for my current 412's, till I found out I had the 11", which they don't make a HD spring for. So I was having to buy new shocks anyway.
I was close to just buying some 412HD, but have read several negative reviews of the 412's poor ride (which I agree with, but I thought it was due to me running them overloaded all the time) and longevity (no idea, bike had 7500 miles when I got it, no ideal how long the 412's had been on it).
I found a really good deal on the 430HD on e-bay. They were listed for $450, had a 15% off e-bay code, and for some reason the seller had an additional 10% off that weekend, so my total cost was $344.
The 430's seem to have better reviews and with the price I got them for, it was a no brainier for me.
, I do find it odd that for a bike that was for sale for 20 years and sold very well that there really is not a lot of shock options out there. It is basically OEM or Progressive for bolt on replacement, or custom if you want to spend the cash for that.