hey-Hey!!!,
Just to save a bit ov room, the MOSFET with its drain connected to B+ is the one that needs heatsinking. The other is only going to have about a volt and a half drain-source, and will not get hot at all.This is sometimes referred to as the 'Top' MSOFET. The 'Bottom' one is the one with its drain connected to the 'upper' source, and its source connected to the R-Set/biasing resistor/pot.
regards,
Douglas