First--I'm a rookie at engine stuff. My 57 has 350 small block bored to 355 with mild cam and gear drive. Has HEI ignition; Had local shop time it with digital timing light; runs good for about 1 mile then starts missing, losing power, then dies. I had it re-timed again figuring the HEI distributor is getting knocked out of correct timing since in sits tight against firewall. Drove it down the road--same thing happens. Could I have a charging issue? Battery issue? I thought it might be a carb adjustment (Edelbrock)but it runs great for the first mile or so. Any help with starting to weed things out appreciated.