This is the Edelbrock "Accu-Gear Drive" system.. for Pontiac V8 from 1955 thru to 79.. but NOT the 301 Pontiac V8 carby OR Turbo series.
Fits: 350, 455, 265, 400, 287, 389, 428, 326, 421, 347.
Edelbrock Accu-Drive timing gear drives won't stretch or wear out, the way timing chains will. They provide up to eight degrees of cam-timing adjustment in two-degree increments and have offset bushings for easy cam indexing, as well as SAE 8620 steel gears that will operate at higher rpms. An Accu-Drive will fit under your stock timing cover and will generate that "gear-whine" sound we all love. Minor machining to the engine block may be required.