1974 Brain Box saves the day.

the small transistor they use today T0-220 is rated at 150W, the TO-3 is rated at 300W and the case is the collector on the TO-3. The 220 has a center pin as Collector or may have only 2 pins and uses the heat sink as the collector, ala TO-3. Either way the TO-220 is just a smaller cheaper version of the TO-3 with less power handling. the TO-3 is not made for pennies anymore and the supporting electronics of the newer boards probably does not spec that high of a power handling capacity. @George Jets your small transistor heat sink should contact the metal of the cover securely to dissipate heat only, probably insulated, not used as the collector circuit anymore for safety reasons (ie. 400V potential at the case of the old ones) you can thread a hole in that heat sink, put some thermal compound on it and screw it down to the real heat sink for added thermal conductivity if your so inclined. Making a new board with that schematic will get you an old style circuit but the switching transistor must be spec'd at the old values to get a 'better' board. Today, a chip can do what 50% of the passives on that circuit can do at about .30 cents.