'75 450SL Idle/Vacuum Help

[350SL4spd]

I just got done doing a front end job on my buddies 450SL (timing chain/gears/rails/tensioner/oil pump & chain/etc/etc; someone waited almost too long to change the chain). She ran like a top before the major surgery. She runs even better now, but lopes @ idle: She'll idle alone perfectly then stumble & miss for a few seconds, then recover & idle fine. Sometimes she'll idle fine for minutes before she stumbles.

I'm betting on a vacuum leak (or intermittent vac leak) somewhere. Where is the best place to look? Or is it more time efficient (in the long run) to just replace all the old vac lines under the hood?

Thanks!
-M-

PS: Can you buy the different color coded vac lines, or do you just replace it all w/ white?