Should be fixable. But why was it overheating in the first place? Idle current may have been set too high due to corroded trimmers. But as there are parts that actually burned, I suspect a short-circuit may have happened. I am sure other experts here can tell you what happened. Start with cleaning the board with a clean paint brush to get rid off all the dust. The damage seems to be only in one area of the board. Find out what the shared denominator is for those four parts to burn up. Then order new replacements. When desoldering on this board, do not use too much heat as you will lift traces. Also - was the transparent plastic holder for the filter capacitors missing, or did you remove it to take the pictures?

Burned output stage. Not a job for an untrained - with all due respect. Repairs like this can give even highly skilled tech guys a good run for their money. Put short - replace everything from the differential amplifier outwards. Then power up slowly using a variac while keeping an eye on the idle current and DC offset. Follow up with adjusting the idle. Martin