Rough idle and takeoff 250 inline

[68gmcdude]

Good evening....
My '68 GMC has an inline 250. It's been running beautifully all summer, including this past Saturday when I took it on a 400 mile, all highway trip to a show. Yesterday I went to go for a ride and now it's idling rough and is rough on takeoff with an occasional backfire. Once up to speed it still runs fine. I changed the points tonight since they looked pretty bad (after only a year) and it didn't help. Tomorrow I'm changing the plugs. What else could it possibly be? Last year I changed everything... Plugs, wires, cap, rotor, points, condenser, coil, carb rebuilt, timed, etc... Thanks!