My original build on the 605 featured the Indy 426SR heads. I ordered them with Indy's CNC option. I later found out they were the first set they CNCd. They were disappointing. I sent them to Modern with instructions to see what he could get out of them. After a couple month delays I finally threatened to show up at his door. He finally finished them and shipped them. Unfortunately all he did was a bowl blend and valve job. They flowed 387@.700.
Anyway they made 853hp@818ftlbs.
Fast forward a couple years and I bought a set of Indy Hi-Po heads 2.4" intakes, 265 cc intake volume. They flowed 443@.700 They made 832 through the mufflers and on previous Dyno pulls the mufflers cost me 117hp. Went to make a couple final pulls with open headers and collectors and my phase convertor that powers the Dyno water pump died. Being short of time I pulled the motor off and reinstalled it in the truck.
I have yet to take it down the track in this configuration. This setup is down almost 100ftlbs but up on hp. The heads moved the hp and tq up 1000 rpm in the power band. Im going to leave it alone until I can get a couple passes in at the strip.