Look at the harmonic balancer. Is it a steel crank, or cast iron? The balancer will tell you. Cast iron will have a counter balance weight on the internal portion of the balancer. Forged steel crank will not. Forged steel...equals high compression. Cast...8:5:1 low compression. As far as the twister package....Just stickers. My '72 has the twister package. All it is, is the dust cloud going down the rear quarter stripes. (NOT UNCOMMON) With 340 numerals beneath it. The only rare option on my 340 duster would be the rocker panel stainless moldings.