John is right. The gear drive is just not necessary. In fact it may even impart detrimental harmonics into the camshaft from the crank causing more valvtrain harmonics that may influence timing events more than any measured chain stretch. This is why all the Pro Stock and Comp Eliminator engines have gone to a belt drive.
My engine is critically close on valve to piston clearance, .058 int/.076 exh and after nearly 6 years of racing it and twisting it to 7200-7500 rpm's I've yet to bang a valve.
Personally I think you get what you pay for and I wouldn't put a $100 gear drive in my engine. YMMV.
