FSA,
After doing this stuff for close to 30 years, I found out a long time ago that the ONLY way to know is to get the actual retainer and locks that you "think" you need and try them.
If they measure ok, then get the springs. Retainers and locks vary all over the place. Also, make sure that the locks you get are from the same manufacturer that the retainers are from. 10 degree locks from one manufacturer will not always fit 10 degree retainers from a different manufacturer. etc etc etc. I have gotten to where I HATE valve springs and retainers
Hardest thing is trying to charge the customer for the time you spend trying to find a combination that will work right with a particular set of heads
I have accumulated about 50 individual retainers of different sizes. That makes things a little easier, having one to try.