If you have to run dual springs for the cam you are using that is true. I'm running a .510 lift solid cam with a Comp 926 single spring. I still had to machine down ( shorten ) the valve guides for retainer to seal clearance though.
Thanks. The cam I was looking at is the Comp cams XS274S: Duration 274/280, Lift .502/.511. So I guess the valve guides will need to be shortened and the heads come of to do so.
