i came out of the driveway last night i goosed it so the tires would turn over then let out. coasted a few feet and their was a loud pop then the truck died wont start back. took it back home to the garage and tried to turn the motor over by hand but it will only go so far then catch. any suggestions on what this could be. i am going to start taking her apart tomorrow. do you think it could be a dropped valve or a broken piston rod or what? please help in any way. or is it telling me that it is time for a 408?

What size pushrods should ia use? Should i go with a double roller timing chain? Would it also be best for me to use arp bolts? any help on anyhting to make it a better motor would be very helpful.