Seeking advice on Crown DC300a speaker amp

Hello folks,
(Schematic attached)

I have a Crown DC300a here. I’ve ordered replacement capacitors for the electrolytics and I’m gonna wire in a single stereo pot instead of the two mono pots.

My goal is to use this in the studio with some bigger JBL 4412 monitors.

It works fine now, but my concerns are as follows.

1. These amps have occasionally been known to blow voice coils, when a transistor fails and you end up with DC on the output.
Is there an easy way/modification to ensure that my speakers are protected? For example, I see in the service manual (too big to attach here but the first thing that comes up when you google DC300a) in one of the diagrams ,that JBL has an inline fuse between the amp and speaker (positive side), I suppose to protect from just this occurrence.  What amperage and wattage for this sort of fuse?

2. The transistors on the back on my amp don’t match any in the DC300a service manual.  These are the driver and output transistors attached to the huge heatsink. In the service manual, we have one version with:

2N3773 Output
2N5804 Drivers

Apparently Crown used a few different transistors during the DC300’s lifetime.

My outputs are labeled:
3990/7652

Drivers are labeled
SJ6387

Looks like several of the output transistors on one channel have been replaced with SJ6451

Anyhow,  if my goal is to use this amp in the studio with some nice JBL’s, I’d like to get both channels balanced obviously, so does anyone know where I can order matched transistors of this sort, or have a recommendation in this regard? Replacements/how to match etc. ??

Thanks