It certainly wouldn't hurt to replace the drain pipes. I think they are readily available.
Make sure that there is a bit of slack in the choke wires so that they are not pulling on the levers when the choke is off.
I believe that you have HD8 carbs? If so, be sure to follow the book procedure on idle adjustment. Especially the part about setting the fast idle screws (stop adjusting screws) front left upper, backed off with the chokes off. I believe it is something like back the adjusting screws out an additional 1.5 turns from just touching the fast idle cams. The throttle butterflys should be completely closed at hot idle. Idle air flow should be adjusted & synchronized with the slow running valves (large screw on the far right front). Start with it backed out about 4 turns.
Adjust idle mixture with the jet adjusting screw, (front left lower). A bit hard to get to.
Sometimes the "cam shoe & rod" the vertical rod that moves up and down with the choke, & in turn raises & lowers the fast idle screw, is sticky & causes problems.
D