If you want a hydraulic roller, the most economical way is to get a later model core that has the valley machined for the holddown spider and the dogbones. Having said that----if you want to run a mech fuel pump you will need a core that is set up for it already or at the minimun has the mount bosses on the casting that can be machined---of course, then the cam core also needs the lobe for the fuel pump---