GFA-5800 repair question

Last week I bought a 5800 because I was considering making a change to my speakers and the ones I'm looking at are low-efficiency/difficult loads.
The amp is in great shape and I've adjusted the bias & offset to specs--and it's stable.
I have one smoked resistor in one zobel so I need to get to the PCBs.
I'd also like to do any "best bang" tweaks but have not turned up any diy mods in my googling.

The heatsink tunnels sure appeared to be easy to remove but with each set of screws I remove I find more that need to be removed. What's the process to pulling the PCBs without dropping hardware into inaccessible areas?
 
Well parts came today so I just replaced the one cooked Zobel.
Couldn't figure out how to free the pcb from the heatsink so I soldered from the top. I hated going the "hack" route but I couldn't find answers anywhere.
I also didn't find any discussion anywhere about applying tweaks to the 5800. 🤷‍♂️