Hi Andy,
one of those ouch moments that we've all had at some point! Thinking it through, as the collector is brought out on the case this is what you will have shorted to the heatsink/chassis/ground. I doubt if that will have harmed the 2N3055 since it wouldn't be conducting in those circumstances, but it will have worried your power supply a bit!
I would check the 2N3055s with a DVM if you have one handy just for reassurance, but the PSU current limiting will have saved your bacon. There will probably be a fault elsewhere in the construction, since it has never actually been proven working at this point. Check through all the component values and their position on the PCBs just in case.
Use your DVM to check voltages on each transistor's terminals and see where that takes you?
BTW your circuit diagram seems a bit generic and the power transistors are not 2N3055s or showing as equivalent in this resource link, so component values could be critical.
https://alltransistors.com/crsearch....fe=10&caps=TO3
Good luck
Chris