1974 duster 440 wont start HELP

I run no less than three ground off the motor to the frame one off the back of the block to the firewall off the front to the frame one from the oil pan to the frame and usually from the alt.bracket to the frame I run my batteries in the trunk the ground to the frame a welded bolt to the frame.and I use 1OT welding lead for the main cable (hot) I know this is over kill but I lost a race in Ohio because car would not start the same dam problem your having.an old friend took a jumper cable from the battery to the frame and the car started up.and I swore I would never have that problem again.I'm not saying that's your trouble but it shour doset hert to have them.....And Ialso make shour the ign.box has a good ground...Artie