Is the engine stock other than the carb? You definitely want to correct the vac leak if you do indeed have one. Since you said “It didn't idle very well before”, it may be time to rebuild the carb as well. You should pull your carb off and re-square the transition slots too. This will ensure it’s idling on the correct circuit. This thread (
http://67-72chevytrucks.com/vboard/s....php?p=7670124) has 2 good pics of the slots on post #37. That whole page really. Your timing is a bit low as well. Bump it up to 12 or 14 initial. Also, hooking up your vac advance correctly affects idle as well. It all works together. As clay68c10 said, make sure the return springs are doing their job.