Got another one! TO-66’s are even harder to get replacements for than TO-3. Again the usual solution is to bodge a TO-220 in place, but the TO-220 tab is much smaller than the TO-66 case, the thermal performance is not as good. This copper heat-spreader + TO-220 transistor should actually offer better thermal performance than the original TO-66; there’s more copper mass overall.

They’re on the way from the fabricator, they should be available in late April.