Right now I can't find my schematic for this amp, but I do recall mine blowing up about 12 years ago and mine burned up those same two resistors.
This was with all of about 10 hours of play time on the amp.

Fortunately it did it at home and to this day I still gig with my 1971 K250 head, talk about a testimonial to build quality!

I just can't recall what more I did back then to fix the whole issue.

I think there are power supply voltage regulators on the left side of the heat sink as seen with the output transistors facing you, might be worth checking those.

What I do recall is that the traces on that board lifted very easily and even with a desoldering station had to jump a few connections back to working.

Give me a few days to think about this.