Did a little tune up this week and replaced a few things, now she’s idling weird and backfiring out the exhaust. 1940 chevy truck has a sbc 350 pulled from a 70 Chevelle. Replaced plugs (delco r45ts, gapped at 40), plug wires (delco 908w), distro cap (delco d308r), rotor (delco c435), pcv valve (standard v178). Also replaced (but surely unrelated) valve covers and valve cover gaskets, master cylinder, pump to carb fuel line and filter, oil and oil filter. Any thoughts or ideas on why it’s idling weird and backfiring so much through the exhaust? Doesn’t sputter or hesitate, and actually acceleration is pretty smooth through second and third gear. wrong plugs? Wrong gap? Etc? It ran fine before I did all of the above. Thanks!