Thanks, RRR. That's funny, my machine shop just installed 901 springs on one set of my cylinder heads. I have Mopar 340 performance springs P4120249 (factory 340 style) for a second set of cylinder heads. Should be interesting to find if I need to clearance either setup (I hope not, don't want to weaken anything). I wonder if the clearance problem is the fault of the retainer (and not the spring diameter).
