Both combos will work w iron heads on pump gas. 10.9: w/ XE284 or 10.4:1 w/ the voodoo. Both put you in the 8.4:1 dynamic range w 170 cranking pressure. Buddy of mine has a 11:1 aluminum headed 400sbc w a comp XE282S solid flat tappit 8.4:1 dynamic comp 170 cranking pressure and it runs good on 91 w 35* total timing and is far from a dog. 485 HP w 500 TQ on the dyno. In a 67 nova that turns 7.10s in the 1/8th and has descent street manors. He owns a machine/speed shop and knows his stuff when it comes to engines.