After some precursory experimentation, I am planing on employing a form of low melting temp solder for use in reworking some very dense, copper core PCB's, both SMT and THT, which were originally mounted with 63/37 solder.
The main problem with these assemblies is that they are designed to be efficient heat-sinks, and as such, do not lend themselves well to typical rework processes or even high-wattage soldering equipment. Further, there are some delicate components nearby (LED's) which can not tolerate heat above 120C for any extended amount of time and the thermagon board material does not share the typical pad adhesion strength o an FR-4 PCB.
The experimentation mentioned was completed with Zephyrtronics "Low Melt" solder. The alloy was used in conjunction with a preheater and temps aroun 100C to cause cometalization to occur between the low melt solder and the 63/37 in order to remove components at lower temperatures than normally possible, hence minimizing the risk of lifting lands and damaging barrels. I have a sample of "Chip Quik" coming in soon as well, but I would like suggestions on similar products to try from those who may be employing something similar or who may be up against similar challenges. The proprietary solutions I mentioned which are marketed as such seem extremely expensive, though we are willing to pay the cost if necessary to save our product.