I also was using that dizzy for a few years (without MSD tho) but as rpm approached 4,500, motor would start to detonate (lost one head gasket at drags due to this). I had it dialled it fairly conservatively and used whatever mech advance in the dizzy to do all the timing. After i went to an EST, with an MSD programmable, i run more timing than what i would have with the old elec dizzy and no detonation at all. There are other people with similar stories of damage due to erratic timing when using these dizzys. If you're keeping it the revs well under that though i cant imagine it being too much of an issue for you?