Then replace "Radio Shack" with "Bob's House of Discount and Crappy Tube Amp Parts". The 'most ludicrous' thing is also the thing that has the absolute least to do with ANYTHING WHATSOEVER. The point is that Radio Shack is known for crappy components. Anyone capable of comprehending English should be able to figure out what I meant.
The only instance of a Dual Rectifier showing up in a Metallica rig is in Hammet's current setup. http://www.encycmet.com/equipment/equipm.shtml In other words... St. Anger tone. That's why I said "Give me a Mark". As in "A Mesa/Boogie guitar amplifier of the Mark I-IV series".
What kind of tube sockets? Good ceramic ones. Has nothing to do with tone, but I've seen too many melted plastic ones to take that chance. Difference in caps? If they're the same Xicon, then nothing. If you're comparing good Xicon caps to the cheapass "400 for $6" grab bags then you're more likely talking about a completely different construction which will undoubtedly lead to different tone (maybe better, maybe worse... who knows?).
You're acting as if caps and resistors are the only components in an amp. They're not. You have to deal with transformers, potentiometers, wire, solder, the quality of your PCB/turrets/eyelets... I'm not one of those "silver mica caps, silver solder, and oxygen free stranded wire" weirdos, but I'm also not a "Screw it, it'll work" kind of guy. Amp construction is no different than guitar construction. Yeah you can get good sounds from lesser quality, but by spending a bit extra and carefully planning what components you're going to use then you will end up with a better sound.
I have a Concert Lead head. I know how loud those little bastards can get. You should post over on the http://www.diypedals.com/ forum and see what they recommend. You should be able to get away with building a high gain pedal, following it with an EQ, then shoving it all in one package with the power amp.