Now you've got me looking for an original MKI Marshall Guv'nor on Ebay. Hmmm now how much should my maximum bid be : )
Good luck with that, they are too pricey for what they are IMO. Distortion is different from overdrive and everyone's taste is different. I have several pedals I like a couple I don't like much. One of my favorites is an old Jordan J-100 pedal, it goes from a little OD, to distortion, to fuzz. I like a stock DS-1 and I like a Tech 21 comp-tortion. Ofcourse you can always spend a lot more on pedals but I get what I need with what I have. I also have an EH English Muff'n, its is OK but I wouldn't by another if I lost it. With some ampsI like to use a Boss Bass EQ pedal, it is great for removing bass flub especially in Fender amps (Custom Vibroux Reverb modded with a switch to add neg feedback, makes it a Vibroverb)... and an 800khz boost gives it a bit of a Marshall feel. Bad Monkey is a decent OD pedal...
You can spend a lot or a little and it can be never ending... almost every pedal I buy is either OD or dist.
I don't know what is in your AC-15 but you might get more of what you want by replacing the first preamp tube with a JJ 12ax7... don't know though.
Good luck!
J