“I am using the Isky 625/626 spring and matching retainers. What is you experience with them and do you know of something better. A friend of mine recently broke one of these springs so I am concerned about failure more than super high RPM.”

I’ve never used the recommend 625/626, IMHO they are only good for road cars, ie, a D grind or .300” lobe lift max gentle road cams that aren’t red lined very often.

The Isky’s I use are P.N. 4205 (Grey & Whites) which are intended for SBC. I set them up with no shims & DIY retainers which give 105-110 lb seat pressure for mild cams or shim them up to the recommended 130+ lb seat pressure for race cams. They have 320 lb/inch rates. My info is 10+ years old now & at the time Isky got sold & their quality dropped so I switched springs. Ended up using springs from the local VW Type1 crowd, a set of duals with similar seat pressure & lift rates that have slightly stiffer outers & slight weaker inners, I was assured that they where Comp Cams or Crane, but am not 100% sure, but they are good. I consider Comp Cams & Crane Cams to be the best in the business. Here is a link to some of Isky’s spring specs, it’s a PDF.