Front Brakes Locking On After Car Idles.

Just checking to see if anyone else has experienced this. Condition is after you start car and let sit and idle for 10 minutes the front brakes will lock on. Let car cool down and brakes will release. Car is a 71 Scamp with recently installed 360, with stock manifolds, power front drum brakes. Before the 360 it had a slant 6 with headers. Never had this problem with that setup. Any suggestions?