There is a very high chance that if you clean the sockets and check the capacitors in the dog house (check for big bulges/blisters at the ends of the caps) and replace those caps (and the bias cap-very important) the amp will work.
I'm not sure the forbon board is melted, it's vulcanized fiberboard and looks very normal for this amp. I have looked inside vintage fenders quite a bit and most of them look like this, my 1ô65 Pro Reverb is like this so like others say, it's probably fine.
Don't go yanking out a bunch of "old parts" off the board!!! They're very likely fine. The cathode bypass capacitors for each preamp triode would be inspected for leaks but you actually have a post 65 here, those black and red dual caps are sealed and do NOT need to be replaced (same goes for all the blue ones).
Those caps (in my experience) started showing up in 66, that combined with the 66 at the end of your chassis ink stamp confirms the suspicion that your amp is a 1966 not 64. The pots will have date codes that also corroborate and the transformer EIA codes will also tell you this.
please do very very little parts replacing if you decide to repair this amp, this is a true vintage blackface fender and throwing parts away inside of the amp just because they're old is insanity.
the only caps that present a danger are the power supply caps and like i said the bias cap (underrated from the factory for some crazy reason). Someone mentioned the death cap and while a failure on that cap could be dangerous, it's a very robust capacitor (sealed blue fender ajax) and doesn't usually need replacing. i do recommend removing it from the circuit anyways as it's dangerous as a failure point. The rest are not safety issues. I'm sure someone will say I'm being nonchalant but trust me, the ones that are a safety issue I am quite pushy about people replacing. i recommend it at all times.
The sound of these parts are a real thing and changing them destroys a very key part of the magical fender sound (yes i know that sounds like bs, i promise it's not!)
Get her running with the bare minimum first, and then chase parts that are problematic. Don't shotgun it! You'll never figure out what's wrong when you finally do start it up. All the changes will throw your voltages way off etc etc.
I hope i have imparted a sense of reverence for the sanctity of the amp, these things are super magical sounding when you play them right. like seriously i can send a clip where residual harmonic content starts to ring out because of the unique characteristics of the carbon comp plate load resistors. it's insane.
please don't gut this amp for a "populated ab763 board". this is the wrong platform for that! you can do that so much cheaper with modern parts and a new chassis from mojo tone (transformers are half or less as expensive as vintage!!!).
like seriously I'll buy it from you to prevent that fate... it's awful and i don't have space for it but that's bordering on whistling diesel destroying Nissan skylines and vintage Toyota hiluxes.
at the end of the day i know it's not my place to tell you what to do with your property but please don't put a wing on that Gran Torino lol
