The purpose of a harmonic dampener is to absorb the high frequency harmonic vibration that can cause fractures or breakage of the crankshaft. The other alternative is to have the engine internally balanced, not an inexpensive proposition. A harmonic damper is hundreds of times cheaper, easier, and also cheap than later replacing a crankshaft etc.

Some good Poly info can be found at the Mopar Muscle website:

[www.moparmusclemagazine.com]

[www.moparmusclemagazine.com]

Note that the above article is 2 parts.

More info here:

[www.1962to1965mopar.ornocar.com]

Also check archived tech info on this Dodge Sweptline website.

[www.dodgesweptline.org]

[www.dodgesweptline.org]

I dearly love the old Polyspehere engines and also vintage Plymouths so I hope all the best to your buddy with his ultra-rare Fury! His should be a 303" engine but could be anywhere from 270" to 318".