Which motor size and brand and type heads ? I've used the stock stamp steel OEM holdowns and bolts on many BB and SB Mopar V8 bracket motors with similar valve spring pressures up to 7000 RPM shruggy If your going for the best holdowns now I would go with steel instead of aluminum due to the rocker shafts being steel so they have similar expansion rates as the motor heats up and no change of tension on the shafts at the holdowns up twocents Studs and nuts with a good quality harden flat steel washers under the nuts between the holdowns are better than bolts also thumbs

Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)