What valve springs should I use?

Well, I ran some SCR and DCR numbers and the DCR is in the 7.2 range with that cam installed straight up (dot-to-dot with a keyways and such perfect)...... it should not be any issue with detonation on 87. That cam is not so long on .050" duration but the ramps are slow and so the .005" duration is relatively long vs. a lot of cams. (But I have used one with even slower ramps than you have....)

Interesting on the reaction to the larger total advance.....

Agreed 1000% on the non-ethanol fuel! But, my son and I found that the Shell V-power ran considerably better in his 10:1 SCR 340 than the local non-ethanol fuel.